Use of the prevalence ratio v the prevalence odds ratio as a measure of risk in cross sectional studies

Association of long working hours and multi-site work-related musculoskeletal disorders among transportation industry workers in Beijing, China

BACKGROUND

Long working hours can lead to a variety of diseases, while the relationship between long work hours and multi-site work-related musculoskeletal disorders (WMSDs) remains unclear. This study aims to explore the association between working hours and multi-site WMSDs.

METHODS

A cross-sectional study was conducted among 2636 transportation industry workers. The Nordic Musculoskeletal Questionnaire was used to assess musculoskeletal disorders. Workers were grouped by weekly working hours (≤ 40 h/wk, 40-55 h/wk, and ≥ 55 h/wk) to compare the prevalence of WMSDs. The correlation between different WMSDs sites and the influencing factors of multi-site WMSDs were analyzed by log-binomial model and logistic regression model.

RESULTS

897 (34.0%) participants faced long working hours. 995 (37.7%) participants suffered from WMSDs, while the highest prevalence of WMSDs symptoms occurred in neck (25.4%), followed by low back (18.4%) and shoulders (14.5%). Wrists WMSDs were associated with WMSDs in necks, shoulders, elbows, hips, and ankles (OR = 2.07-8.01). According to binary and multivariate logistic regression, the risk of WMSDs was higher in participants who worked 40-55 h/wk (OR: 1.30, 95% CI: 1.09-1.56) and more than 55 h/wk (OR: 2.15, 95% CI: 1.46-3.16) compared to participants who worked less than 40 h/wk. Additionally, participants who worked 40-55 h/wk (OR: 1.39, 95% CI: 1.09-1.78) and more than 55 h/wk (OR: 2.92, 95% CI: 1.82-4.70) were more likely to suffer from WMSDs in three or more sites.

CONCLUSION

Long working hours were positively associated with multi-site WMSDs. Early preventive and management measures of long working hours and WMSDs are of importance.

Sex Difference and Socioeconomic Inequity in Chinese People With Hypertension: National Cross-Sectional Survey Study

Background

Sex differences in blood pressure (BP) levels and hypertension are important and the role of socioeconomic status (SES) in sex differences in hypertension remains unclear.

Objective

This study aimed to evaluate the impact of SES on sex differences of hypertension in a nationally representative survey study.

Methods

A total of 98,658 participants aged ≥18 years who have lived in their current residence for ≥6 months were recruited from 162 study sites across mainland China. Sex was self-reported. Individual-level SES included the highest level of education and annual household income. Area-level SES included economic development status, urban/rural residency, and north/south location. Outcomes included levels of systolic and diastolic BP, and hypertension. Linear and Cox regression models were used to examine the associations between sex (women vs men) and BP characteristics stratified by individual or combined SES indicators.

Results

Systolic and diastolic BP levels and the prevalence of hypertension were higher in men than in women. This sex difference was found across categories of SES with widened sex disparities in participants having more favorable SES. Significant multiplicative interaction effects of SES on the association of sex with BP characteristics were found. Women with improving SES were associated with lower BP and hypertension prevalence compared to men. For combined SES, a 9% (prevalence ratio 0.91, 95% CI 0.83-0.98) and a 30% lower probability (prevalence ratio 0.70, 95% CI 0.63-0.78) of having hypertension were found in women with an overall intermediate SES and high SES, respectively, compared to those with low SES, while no significant reduction was found in men.

Conclusions

There are significant sex differences in BP characteristics and SES has a potent impact on the disparities. Sex-specific public health policies to alleviate socioeconomic inequalities, especially in women are important for the prevention of hypertension.

Do dietary practices and household environmental quality mediate socio-economic inequalities in child undernutrition risk in West Africa?

OBJECTIVE

We investigated the relationship between socio-economic status and child undernutrition in West Africa (WA), and further examined the mediating role of dietary practices (measured as minimum dietary diversity (MDD), minimum meal frequency (MMF) and minimum acceptable diet (MAD)) and household environmental quality (HEQ) in the observed relationship.

DESIGN

Thirteen countries were included in the study. We leveraged the most recent Demographic and Health Surveys datasets ranging from 2010 to 2019. Poisson regression model with robust standard errors was used to estimate prevalence ratios and their corresponding 95 % CI. Structural equation modelling was used to conduct the mediation analysis.

SETTING

West Africa.

PARTICIPANTS

132 448 under-five children born within 5 years preceding the survey were included.

RESULTS

Overall, 32·5 %, 8·2 %, 20·1 % and 71·7 % of WA children were stunted, wasted, underweight and anaemic, respectively. Prevalence of undernutrition decreased with increasing maternal education and household wealth (Trend P-values < 0·001). Secondary or higher maternal education and residence in rich households were associated with statistically significant decrease in the prevalence of stunting, wasting, underweight and anaemia among children in WA. MAD was found to mediate the association of low maternal education and poor household wealth with childhood stunting and underweight by 35·9 % to 44·5 %. MDD, MMF and HEQ did not mediate the observed relationship.

CONCLUSIONS

The study findings enables an evaluation and improvement of existing intervention strategies through a socio-economic lens to help address the high burden of child undernutrition in WA and other developing regions.

Ever Smoking is Not Associated with Performed Spirometry while Occupational Exposure and Respiratory Symptoms are

Objective

Despite recommendations, assessment using spirometry or peak expiratory flow is insufficient in the clinical evaluation of suspected obstructive pulmonary disease. The aim was to investigate factors associated with performing spirometry or peak flow expiratory flow assessment.

Methods

Randomly selected subjects from the general population aged 50-65 completed a respiratory questionnaire with items about the history of previously performed spirometry or peak expiratory flow. The association between ever having had spirometry or peak expiratory flow performed was analyzed for smoking, age, sex, occupational exposures, dyspnea, wheeze, self-reported physician diagnosed asthma and COPD using multivariable logistic regression models. The results are presented as odds ratios (OR) with 95% confidence intervals (95% CIs).

Results

Of the 1105 participants, 43.4% (n=479) had a history of previously performed spirometry or peak expiratory flow. Occupational exposure (OR 1.72, [95% CI] 1.30-2.27), wheeze (OR 2.29, 1.41-3.70), and dyspnea (OR 1.70, 1.11-2.60) were associated with previously performed spirometry. Compared to men, women had spirometry or peak expiratory flow performed less often (OR 0.67, 0.51-0.86). Neither current smoking (OR 0.83, 0.57-1.20) or former smoking (OR 1.27, 0.96-1.67) were associated with performed spirometry or peak expiratory flow.

Conclusion

We found no relation between smoking status and a history of previously performed spirometry or peak expiratory flow in a population-based sample of middle-aged people. This is surprising regarding the strong guidelines which highlight the importance for spirometry surveillance on current smokers due to their increased risk of lung disease. Male sex, respiratory symptoms and occupational exposures to air pollution were associated with previously performed spirometry or peak expiratory flow. The association with occupational exposure may be an effect of pre-employment screening and workplace surveillance, and the findings indicate that females do not receive the same attention regarding spirometry or peak expiratory flow.

Land use impacts on parasitic infection: a cross-sectional epidemiological study on the role of irrigated agriculture in schistosome infection in a dammed landscape

Background

Water resources development promotes agricultural expansion and food security. But are these benefits offset by increased infectious disease risk? Dam construction on the Senegal River in 1986 was followed by agricultural expansion and increased transmission of human schistosomes. Yet the mechanisms linking these two processes at the individual and household levels remain unclear. We investigated the association between household land use and schistosome infection in children.

Methods

We analyzed cross-sectional household survey data (n = 655) collected in 16 rural villages in August 2016  across demographic, socio-economic and land use dimensions, which were matched to Schistosoma haematobium (n = 1232) and S. mansoni (n = 1222) infection data collected from school-aged children. Mixed effects regression determined the relationship between irrigated area and schistosome infection presence and intensity.

Results

Controlling for socio-economic and demographic risk factors, irrigated area cultivated by a household was associated with an increase in the presence of S. haematobium infection (odds ratio [OR] = 1.14; 95% confidence interval [95% CI]: 1.03–1.28) but not S. mansoni infection (OR = 1.02; 95% CI: 0.93–1.11). Associations between infection intensity and irrigated area were positive but imprecise (S. haematobium: rate ratio [RR] = 1.05; 95% CI: 0.98–1.13, S. mansoni: RR = 1.09; 95% CI: 0.89–1.32).

Conclusions

Household engagement in irrigated agriculture increases individual risk of S. haematobium but not S. mansoni infection. Increased contact with irrigated landscapes likely drives exposure, with greater impacts on households relying on agricultural livelihoods.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40249-021-00816-5.

Changes to cardiovascular risk factors over 7 years: a prospective cohort study of in situ urbanised residents in the Chaoyang District of Beijing

OBJECTIVES

To examine changes in cardiovascular risk factors of in situ urbanised residents between 2010 and 2017.

DESIGN

Population-based cohort study.

SETTING

The Chaoyang District of Beijing, China.

PARTICIPANTS

A total of 942 in situ urbanised rural residents aged 35-64 who participated in the cardiovascular disease (CVD) risk factors study in China between 2010 and 2017.

MAIN OUTCOME MEASURES

Lifestyles (smoking, drinking and effective exercise) and medical history (diabetes, hypertension, dyslipidaemia, overweight and obesity) were self-reported. New cases of diabetes, hypertension, dyslipidaemia, overweight and obesity were confirmed by physical examination or blood biochemical tests. Multiple linear regression and log-binomial models analyses adjusted for sociodemographic confounders were conducted to evaluate any changes of clinical indexes and to estimate prevalence rate ratios (PRRs), respectively.

RESULTS

During the study period of 2010-2017, diastolic blood pressure elevated by 3.55 mm Hg, central blood pressure increased by 4.39 mm Hg, total cholesterol decreased by 0.29 mmol/L and hypertension increased significantly (PRR=1.25, p<0.05) after adjusting for demographic, lifestyle and family history factors. Effective exercise rate (PRR=1.57), prevalence of diabetes (PRR=1.36) and dyslipidaemia (PRR=1.19) all increased from 2010 to 2017. However, these changes were not significant after adjusting for confounders (p>0.05). Prevalence of smoking, drinking, hypertension, overweight and obesity was significantly higher in males than females in both 2010 and 2017. In 2017, the 10-year risk of atherosclerotic CVD increased in 29.8% of participants and decreased in 6.1% of individuals.

CONCLUSIONS

CVD risk factors augmented remarkably for in situ urbanised rural residents aged 35-64 in the Chaoyang District of Beijing, especially those indicators related to blood pressure. Awareness of the direction and magnitude of these risk factor changes may be beneficial in informing targeted strategies for preventing CVDs of in situ urbanised populations.

Prevalence and risk factors of postpartum depression within one year after birth in urban slums of Dhaka, Bangladesh

Postpartum depression (PPD) is a serious pubic health concern and known to have the adverse effects on mother’s perinatal wellbeing; and child’s physical and cognitive development. There were limited literatures on PPD in Bangladesh, especially in urban slum context. The aim of this study was to assess the burden and risk factors of PPD among the urban slum women. A cross-sectional study was conducted between November-December 2017 in three urban slums on 376 women within first 12 months of postpartum. A validated Bangla version of Edinburgh Postnatal Depression Scale was used to measure the depression status. Respondent’s socio-economic characteristics and other risk factors were collected with structured validated questionaire by trained interviewers. Unadjusted Prevalence Ratio (PR) and Adjusted Prevalence Ratio (APR) were estimated with Generalized Linear Model (GLM) and Generalized Estimating Equation (GEE) respectively to identify the risk factors of PPD. The prevalence of PPD was 39.4% within first 12 months following the child birth. Job involvement after child delivery (APR = 1.9, 95% CI = 1.1, 3.3), job loss due to pregnancy (APR = 1.5, 95% CI = 1.0, 2.1), history of miscarriage or still birth or child death (APR = 1.4, 95% CI = 1.0, 2.0), unintended pregnancy (APR = 1.8, 95% CI = 1.3, 2.5), management of delivery cost by borrowing, selling or mortgaging assets (APR = 1.3, 95% CI = 0.9, 1.9), depressive symptom during pregnancy (APR = 2.5, 95% CI = 1.7, 3.8) and intimate partner violence (APR = 2.0, 95% CI = 1.2, 3.3), were identified as risk factors. PPD was not associated with poverty, mother in law and any child related factors. The burden of postpartum depression was high in the urban slum of Bangladesh. Maternal mental health services should be integrated with existing maternal health services. Research is required for the innovation of effective, low cost and culturally appropriate PPD case management and preventive intervention in urban slum of Bangladesh.

Treatment gap, help-seeking, stigma and magnitude of alcohol use disorder in rural Ethiopia

BACKGROUND

Although alcohol use disorders contribute a high proportion of population disease burden, the treatment gap is large, especially in low- and middle-income countries. To narrow this gap, contextually relevant evidence is needed to inform service development in low- and middle-income country settings. The aim of this study was to assess the magnitude of the treatment gap for alcohol use disorder, help-seeking behavior, stigma and barriers to care among people with alcohol use disorder in rural Ethiopia.

METHODS

A cross-sectional, house-to-house survey was conducted in Sodo district, south Ethiopia. A sample of 1500 adults was selected using simple random sampling from a census of households and screened for alcohol use disorder using the alcohol use disorders identification tool (AUDIT). Help-seeking, barriers to care and internalized stigma were investigated among people with moderately severe alcohol use disorder (AUDIT score ≥ 16). Poisson regression with robust variance was used to examine factors associated with alcohol use disorder.

RESULTS

The prevalence of alcohol use disorder (AUDIT ≥8) in the past 12 months was 13.9% (25.8% in men and 2.4% in women, p-value < 0.001). People with alcohol use disorder had increased disability (adjusted prevalence ratio (aPR) 1.03, 95% confidence interval (CI) 1.01, 1.03) and higher depressive symptom scores (aPR 1.02, 95% CI 1.01, 1.04). The treatment gap was very wide, about 87.0% (only 13% sought help) of participants with an AUDIT score ≥ 16 had never sought help for their alcohol problems and 70.0% reported high internalized stigma. Major barriers to seeking help were wanted to handle the problem on their own, believing that it would get better by itself and being unsure about where to go.

CONCLUSIONS

Although alcohol use disorders are common problems in Ethiopian community, the unmet need for treatment is substantial. An integrated care approach has the potential to address this need, but stigma and low awareness may be major barriers to help-seeking. Interventions to reduce stigma and enhance community awareness are recommended.

Low use of artemisinin-based combination therapy for febrile children under five and barriers to correct fever management in Benin: a decade after WHO recommendation

Background

Artemisinin-based combination therapy (ACT), used to treat uncomplicated malaria cases, is one of the main strategies of malaria control and elimination. One of the main objectives of the Benin National Malaria Control Program’s (NMCP) strategic plan is to ensure that at least 80% of uncomplicated malaria is treated with ACT within 24 h. Therefore, it was of great interest to measure whether the country case management of fever amongst children under five, adhered to the NMCP’s strategic plan and look into the barriers to the use of ACT.

Methods

A cross-sectional survey based on a cluster and multi-stage sampling was conducted in two rural health districts in Benin. We recruited 768 and 594 children under five years were included in the northern and in the southern respectively. Data was collected on the general use of ACT and on the correct use of ACT that adheres to the NMCP’s strategy, as well as the barriers that prevent the proper management of fever amongst children. To assess the certain predictors of ACT usage, logistic regression was used, while taking into account the cluster random effect.

Results

Among febrile children aged 6 to 59 months, 20.7% in the south and 33.9% in north received ACT. The correct use of ACT, was very low, 5.8% and in southern and 8.6% northern areas. Caregivers who received information on ACT were 3.13 time more likely in the south and 2.98 time more likely in the north to give ACT to their feverish child, PPR = 3.13[1.72–4.15] and PPR = 2.98 [2.72–3.11] respectively. Chloroquine and quinine, other malaria treatments not recommended by NMCP, were still being used in both areas: 12.3 and 3.3% in the south and 11.4 and 3.0% in the north.

Conclusion

In Benin, the use and the correct use of ACT for febrile children remains low. The study also showed that having received information about the use of ACT is positively associated with the use of ACT. This point highlights the fact that efforts may not have been sufficiently integrated with social communication, which should be based on the behavioural determinants of populations.

Electronic supplementary material

The online version of this article (10.1186/s12889-018-5077-6) contains supplementary material, which is available to authorized users.

Metabolic syndrome and masked hypertension among African Americans: The Jackson Heart Study

The metabolic syndrome is associated with higher ambulatory blood pressure. The authors studied the association of metabolic syndrome and masked hypertension (MHT) among African Americans with clinic-measured systolic/diastolic blood pressure (SBP/DBP) <140/90 mm Hg in the Jackson Heart Study. MHT was defined as daytime, nighttime, or 24-hour hypertension on ambulatory blood pressure monitoring. Among 359 participants not taking antihypertensive medication, the metabolic syndrome was associated with MHT (prevalence ratio, 1.38; 95% confidence interval, 1.10-1.74]). When metabolic syndrome components (clinic SBP/DBP 130-139/85-89 mm Hg, abdominal obesity, impaired glucose, low high-density lipoprotein cholesterol, high triglycerides) were analyzed separately, only clinic SBP/DBP 130-139/85-89 mm Hg was associated with MHT (prevalence ratio, 1.90; 95% confidence interval, 1.56-2.32]). The metabolic syndrome was not associated with MHT among participants not taking antihypertensive medication with SBP/DBP 130-139/85-89 and <130/85 mm Hg, separately, or among participants taking antihypertensive medication (n=393). Ambulatory blood pressure monitoring screening for MHT among African Americans should be considered based on clinic BP, not metabolic syndrome.

Exact inference for the risk ratio with an imperfect diagnostic test

The risk ratio quantifies the risk of disease in a study population relative to a reference population. Standard methods of estimation and testing assume a perfect diagnostic test having sensitivity and specificity of 100%. However, this assumption typically does not hold, and this may invalidate naive estimation and testing for the risk ratio. We propose procedures that control for sensitivity and specificity of the diagnostic test, given the risks are measured by proportions, as it is in cross-sectional studies or studies with fixed follow-up times. These procedures provide an exact unconditional test and confidence interval for the true risk ratio. The methods also cover the case when sensitivity and specificity differ in the two groups (differential misclassification). The resulting test and confidence interval may be useful in epidemiological studies as well as in clinical and vaccine trials. We illustrate the method with real-life examples which demonstrate that ignoring sensitivity and specificity of the diagnostic test may lead to considerable bias in the estimated risk ratio.

Factors affecting adherence to national malaria treatment guidelines in management of malaria among public healthcare workers in Kamuli District, Uganda

Background

Malaria remains a major public health threat accounting for 30.4 % of disease morbidity in outpatient clinic visits across all age groups in Uganda. Consequently, malaria control remains a major public health priority in endemic countries such as Uganda. Experiences from other countries in Africa that revised their malaria case management suggest that health workers adherence may be problematic.

Methods

A descriptive, cross-sectional design was used and collected information on health system, health workers and patients. Using log-binomial regression model, adjusted prevalence risk ratios (PRRs) and their associated 95 % confidence intervals were determined in line with adherence to new treatment guidelines of parasitological diagnosis and prompt treatment with artemisinin combination therapy (ACT).

Results

Nine health centres, 24 health workers and 240 patient consultations were evaluated. Overall adherence to national malaria treatment guidelines (NMTG) was 50.6 % (122/241). It was significantly high at HC III [115 (53 %)] than at HC IV (29 %) [PRR = 0.28 (95 % CI 0.148 0.52), p = 0.000]. Compared to the nursing aide, the adherence level was 1.57 times higher among enrolled nurses (p = 0.004) and 1.68 times higher among nursing officers, p = 0.238, with statistical significance among the former. No attendance of facility malaria-specific continuing medical education (CME) sessions [PRR = 1.9 (95 % CI 1.29 2.78), p = 0.001] and no display of malaria treatment job aides in consultation rooms [PRR = 0.64 (95 % CI 0.4 1.03), p = 0.07] was associated with increased adherence to guidelines with the former showing a statistical significance and the association of the latter borderline statistical significance. The adherence was higher when the laboratory was functional [PRR = 0.47 (95 % CI 0.35 0.63)] when the laboratory was functional in previous 6 months. Age of health worker, duration of employment, supervision, educational level, and age of patient were found not associated with adherence to new treatment guidelines.

Conclusion

Adherence to malaria treatment guidelines in Uganda is sub-optimal. There is an urgent need for deliberate interventions to improve adherence to these guidelines. Possible interventions to be explored should include: provision of job aides and improved access to laboratory services. There is also a need for continuous medical educational sessions for health workers, especially those at higher-level facilities and higher cadres, on adherence to guidelines in management of fever, including management of other causes of fever.

Sexual Risk Behaviours and Willingness to Be Circumcised among Uncircumcised Adult Men in Uganda

Background

There has been substantial demand for safe male circumcision (SMC) in Uganda in the early programme scale-up phase. Research indicates that early adopters of new interventions often differ from later adopters in relation to a range of behaviours. However, there is limited knowledge about the risk profile of men who were willing to be circumcised at the time of launching the SMC programme, i.e., potential early adopters, compared to those who were reluctant. The aim of this study was to address this gap to provide indications on whether it is likely that potential early adopters of male circumcision were more in need of this new prevention measure than others.

Methods

Data were from the 2011 Uganda AIDS Indictor Survey (UAIS), with a nationally representative sample of men 15 to 59 years. The analysis was based on generalized linear models, obtaining prevalence risk ratios (PRR) with 95% confidence intervals (CI) as measures of association between willingness to be circumcised and multiple sexual partners, transactional sex, non-marital sex and non-use of condoms at last non-marital sex.

Results

Of the 5,776 men in the survey, 44% expressed willingness to be circumcised. Willingness to be circumcised was higher among the younger, urban and educated men. In the unadjusted analyses, all the sexual risk behaviours were associated with willingness to be circumcised, while in the adjusted analysis, non-marital sex (Adj PRR 1.27; CI: 1.16–1.40) and non-use of condoms at last such sex (Adj PRR 1.18; CI: 1.07–1.29) were associated with higher willingness to be circumcised.

Conclusion

Willingness to be circumcised was relatively high at the launch of the SMC programme and was more common among uncircumcised men reporting sexual risk behaviours. This indicates that the early adopters of SMC were likely to be in particular need of such additional HIV protective measures.

Obtaining adjusted prevalence ratios from logistic regression models in cross-sectional studies

In the last decades, the use of the epidemiological prevalence ratio (PR) instead of the odds ratio has been debated as a measure of association in cross-sectional studies. This article addresses the main difficulties in the use of statistical models for the calculation of PR: convergence problems, availability of tools and inappropriate assumptions. We implement the direct approach to estimate the PR from binary regression models based on two methods proposed by Wilcosky & Chambless and compare with different methods. We used three examples and compared the crude and adjusted estimate of PR, with the estimates obtained by use of log-binomial, Poisson regression and the prevalence odds ratio (POR). PRs obtained from the direct approach resulted in values close enough to those obtained by log-binomial and Poisson, while the POR overestimated the PR. The model implemented here showed the following advantages: no numerical instability; assumes adequate probability distribution and, is available through the R statistical package.

Maternal, care provider, and institutional-level risk factors for early term elective repeat cesarean delivery: a population-based cohort study

To identify maternal, care provider, and institutional-level risk factors for early term (37-38 weeks) elective repeat cesarean delivery in a population-based cohort. Retrospective cohort study of women in the British Columbia (BC) Perinatal Data Registry, BC, Canada, 2008-2011, with an elective repeat cesarean delivery at term. Absolute percent differences (risk differences) in early term delivery rates were calculated according to maternal characteristics, type of care provider, calendar time (day of the week, time of year), and annual institutional obstetrical volume. Of the 7,687 elective repeat cesareans at term in BC, 55 % occurred before 39 + 0 weeks. Early term delivery was significantly more common with multiple previous cesareans [8.2 percentage points (95 % CI 5.5, 10.9) for 2 previous cesareans, 11.3 (95 % CI 5.1, 17.4) for 3 or more previous cesareans], obesity [6.7 percentage points (95 % CI 1.6, 11.7)], and a hospital obstetrical volume <2,500 deliveries per year. Type of care provider and calendar time were not significant risk factors for early term delivery. Early term elective repeat cesarean was common across a wide range of maternal, care provider, and institutional characteristics, suggesting that most obstetrical care settings would benefit from quality-improvement programs to reduce elective repeat cesarean deliveries before 39 weeks. A better understanding of the risks and benefits of early term delivery among obese women and women with multiple previous cesareans is needed given the higher rates of early term delivery observed in these women.

Potential biases in the classification, analysis and interpretations in cross-sectional study: commentaries - surrounding the article "resting heart rate: its correlations and potential for screening metabolic dysfunctions in adolescents"

BACKGROUND

Resting heart rate reflects sympathetic nerve activity. A significant association between resting heart rate (HR) and all causes of cardiovascular mortality has been reported by some epidemiologic studies. Despite suggestive evidence, resting heart rate (RHR) has not been formally explored as a prognostic factor and potential therapeutic outcome and, therefore, is not generally accepted in adolescents.

DISCUSSION

The core of the debate is the methodological aspects used in "Resting heart rate: its correlations and potential for screening metabolic dysfunctions in adolescents"; the points are: cutoff used for cluster RHR, two different statistical models used to analyze the same set of variables, one for continuous data, and another for categorical data; interpretation of p-value < 0.05, sampling process involving two random stages, analysis of design effect and the parameters of screening tests.

SUMMARY

Aspects that must be taken into account for evaluation of a screening test to measure the potential for discrimination for a common variable (population with outcome vs. no outcome population), the main indicators are: sensitivity, specificity, accuracy, positive predictive value and negative predictive value. The measures of argumentation equality (CI) or difference (p-valor) are important to validate these indicators but do not indicate quality of screening.

Maternal awareness of young children's physical activity: levels and cross-sectional correlates of overestimation

BACKGROUND

Factors associated with parental awareness of children's physical activity (PA) levels have not been explored in preschool-aged children. This paper investigates maternal awareness of preschool-aged children's PA levels and determined correlates associated with maternal overestimation of PA.

METHODS

Data from the Southampton Women's Survey, a UK population-based study, were collected March 2006 through June 2009. Daily minutes of moderate-to-vigorous PA (MVPA) were derived using accelerometry in 478 4-year-old children. Mothers who were realistic or overestimated their child's PA were identified. Log-binomial regression was used to analyse correlates of maternal overestimation of PA levels in children whose mothers perceived them to be active (n = 438).

RESULTS

40.8% of children were classified as inactive: 89.7% of these were perceived to be active by their mothers (over-estimators). These mothers were more likely to think their child sometimes lacked skills required to be physically active (RR (95% CI) = 1.29(1.03-1.63)) and their child was more likely to attend nursery full-time (RR = 1.53(1.14-2.04)). They were less likely to have older children at home (RR = 0.71(0.56-0.90)).

CONCLUSIONS

Almost 90% of mothers of inactive preschool-aged children perceive their child to be active. Nursery-school attendance and having older siblings at home may be important to consider when designing behavioural interventions to increase PA in preschool children.

Accounting for misclassified outcomes in binary regression models using multiple imputation with internal validation data

Outcome misclassification is widespread in epidemiology, but methods to account for it are rarely used. We describe the use of multiple imputation to reduce bias when validation data are available for a subgroup of study participants. This approach is illustrated using data from 308 participants in the multicenter Herpetic Eye Disease Study between 1992 and 1998 (48% female; 85% white; median age, 49 years). The odds ratio comparing the acyclovir group with the placebo group on the gold-standard outcome (physician-diagnosed herpes simplex virus recurrence) was 0.62 (95% confidence interval (CI): 0.35, 1.09). We masked ourselves to physician diagnosis except for a 30% validation subgroup used to compare methods. Multiple imputation (odds ratio (OR) = 0.60; 95% CI: 0.24, 1.51) was compared with naive analysis using self-reported outcomes (OR = 0.90; 95% CI: 0.47, 1.73), analysis restricted to the validation subgroup (OR = 0.57; 95% CI: 0.20, 1.59), and direct maximum likelihood (OR = 0.62; 95% CI: 0.26, 1.53). In simulations, multiple imputation and direct maximum likelihood had greater statistical power than did analysis restricted to the validation subgroup, yet all 3 provided unbiased estimates of the odds ratio. The multiple-imputation approach was extended to estimate risk ratios using log-binomial regression. Multiple imputation has advantages regarding flexibility and ease of implementation for epidemiologists familiar with missing data methods.

Diabetes mellitus and its correlates in an Iranian adult population

The rising epidemic of diabetes imposes a substantial economic burden on the Middle East. Using baseline data from a population based cohort study, we aimed to identify the correlates of diabetes mellitus (DM) in a mainly rural population from Iran. Between 2004 and 2007, 50044 adults between 30 and 87 years old from Golestan Province located in Northeast Iran were enrolled in the Golestan Cohort Study. Demographic and health-related information was collected using questionnaires. Individuals' body sizes at ages 15 and 30 were assessed by validated pictograms ranging from 1 (very lean) to 7 in men and 9 in women. DM diagnosis was based on the self-report of a physician's diagnosis. The accuracy of self-reported DM was evaluated in a subcohort of 3811 individuals using fasting plasma glucose level and medical records. Poisson regression with robust variance estimator was used to estimate prevalence ratios (PR's). The prevalence of self-reported DM standardized to the national and world population was 5.7% and 6.2%, respectively. Self-reported DM had 61.5% sensitivity and 97.6% specificity. Socioeconomic status was inversely associated with DM prevalence. Green tea and opium consumption increased the prevalence of DM. Obesity at all ages and extreme leanness in childhood increased diabetes prevalence. Being obese throughout life doubled DM prevalence in women (PR: 2.1; 95% CI: 1.8, 2.4). These findings emphasize the importance of improving DM awareness, improving general living conditions, and early lifestyle modifications in diabetes prevention.

Prevalence and determinants of Helicobacter pylori sero-positivity in the Australian adult community

BACKGROUND AND AIM

  To estimate the sero-prevalence of Helicobacter Pylori infection in the Australian adult population and identify determinants.

METHODS

  We analyzed serum samples and questionnaire data from 1355 community controls who participated in a nationwide case-control study of esophageal cancer in Australia between 2002 and 2005. We estimated the prevalence ratio and 95% confidence interval using log binomial regression models.

RESULTS

  The age and sex standardized sero-prevalence of H. pylori was 15.5%. The prevalence of infection varied significantly with age, ranging from 5% (< 40 years) to 32% (≥ 70 years). H. pylori infection was significantly higher among those born overseas (prevalence ratio [PR] 1.63; 95% confidence interval [CI] 1.34-1.98) compared with those born in Australia or New Zealand. H. pylori sero-prevalence was 23% higher among participants living in the lowest quartile of socio-economic areas (PR 0.77; 95%CI 0.59-0.99 for Q4 compared with Q1). H pylori serostatus was significantly inversely associated with university education (PR 0.56; 95%CI 0.38-0.83), frequent reflux symptoms (PR 0.62; 95%CI 0.42-0.91), use of proton pump inhibitor (PR 0.69; 95%CI 0.48-0.98) and use of medications for gut spasms (PR 0.48; 95%CI 0.25-0.93). H. pylori serostatus was not associated with body mass index, smoking, alcohol or physical activity.

CONCLUSIONS

  The prevalence of H. pylori infection in Australian adults is lower than other developed countries. H. pylori infection is most common among those living in the areas of socio-economic disadvantage or who were born overseas.

Measures and models for causal inference in cross-sectional studies: arguments for the appropriateness of the prevalence odds ratio and related logistic regression

Background

Several papers have discussed which effect measures are appropriate to capture the contrast between exposure groups in cross-sectional studies, and which related multivariate models are suitable. Although some have favored the Prevalence Ratio over the Prevalence Odds Ratio -- thus suggesting the use of log-binomial or robust Poisson instead of the logistic regression models -- this debate is still far from settled and requires close scrutiny.

Discussion

In order to evaluate how accurately true causal parameters such as Incidence Density Ratio (IDR) or the Cumulative Incidence Ratio (CIR) are effectively estimated, this paper presents a series of scenarios in which a researcher happens to find a preset ratio of prevalences in a given cross-sectional study. Results show that, provided essential and non-waivable conditions for causal inference are met, the CIR is most often inestimable whether through the Prevalence Ratio or the Prevalence Odds Ratio, and that the latter is the measure that consistently yields an appropriate measure of the Incidence Density Ratio.

Summary

Multivariate regression models should be avoided when assumptions for causal inference from cross-sectional data do not hold. Nevertheless, if these assumptions are met, it is the logistic regression model that is best suited for this task as it provides a suitable estimate of the Incidence Density Ratio.

A Practical Guide for Multivariate Analysis of Dichotomous Outcomes

A dichotomous (2-category) outcome variable is often encountered in biomedical research, and Multiple Logistic Regression is often deployed for the analysis of such data. As Logistic Regression estimates the Odds Ratio (OR) as an effect measure, it is only suitable for case-control studies. For cross-sectional and time-to-event studies, the Prevalence Ratio and Cumulative Incidence Ratio can be estimated and easily interpreted. The logistic regression will produce the OR which is difficult to interpret in these studies. In this report, we reviewed 3 alternative multivariate statistical models to replace Logistic Regression for the analysis of data from cross-sectional and time-to-event studies, viz, Modified Cox Proportional Hazard Regression Model, Log-Binomial Regression Model and Poisson Regression Model incorporating the Robust Sandwich Variance. Although none of the models is without flaws, we conclude the last model is the most viable. A numeric example is given to compare the statistical results obtained from all 4 models. Key words: Alternatives to logistic regression, Cross-sectional studies, Risk ratio vs odds ratio

Association between neighborhood safety and overweight status among urban adolescents

Background

Neighborhood safety may be an important social environmental determinant of overweight. We examined the relationship between perceived neighborhood safety and overweight status, and assessed the validity of reported neighborhood safety among a representative community sample of urban adolescents (who were racially and ethnically diverse).

Methods

Data come from the 2006 Boston Youth Survey, a cross-sectional study in which public high school students in Boston, MA completed a pencil-and-paper survey. The study used a two-stage, stratified sampling design whereby schools and then 9^th–12^th grade classrooms within schools were selected (the analytic sample included 1,140 students). Students reported their perceptions of neighborhood safety and several associated dimensions. With self-reported height and weight data, we computed body mass index (BMI, kg/m²) for the adolescents based on CDC growth charts. Chi-square statistics and corresponding p-values were computed to compare perceived neighborhood safety by the several associated dimensions. Prevalence ratios (PRs) and 95% confidence intervals (CI) were calculated to examine the association between perceived neighborhood safety and the prevalence of overweight status controlling for relevant covariates and school site.

Results

More than one-third (35.6%) of students said they always felt safe in their neighborhood, 43.9% said they sometimes felt safe, 11.6% rarely felt safe, and 8.9% never felt safe. Those students who reported that they rarely or never feel safe in their neighborhoods were more likely than those who said they always or sometimes feel safe to believe that gang violence was a serious problem in their neighborhood or school (68.0% vs. 44.1%, p < 0.001), and to have seen someone in their neighborhood assaulted with a weapon (other than a firearm) in the past 12 months (17.8% vs. 11.3%, p = 0.025). In the fully adjusted model (including grade and school) stratified by race/ethnicity, we found a statistically significant association between feeling unsafe in one's own neighborhood and overweight status among those in the Other race/ethnicity group [(PR = 1.56, (95% CI: 1.02, 2.40)].

Conclusion

Data suggest that perception of neighborhood safety may be associated with overweight status among urban adolescents in certain racial/ethnic groups. Policies and programs to address neighborhood safety may also be preventive for adolescent overweight.

Estimating adjusted prevalence ratio in clustered cross-sectional epidemiological data

Background

Many epidemiologic studies report the odds ratio as a measure of association for cross-sectional studies with common outcomes. In such cases, the prevalence ratios may not be inferred from the estimated odds ratios. This paper overviews the most commonly used procedures to obtain adjusted prevalence ratios and extends the discussion to the analysis of clustered cross-sectional studies.

Methods

Prevalence ratios(PR) were estimated using logistic models with random effects. Their 95% confidence intervals were obtained using delta method and clustered bootstrap. The performance of these approaches was evaluated through simulation studies. Using data from two studies with health-related outcomes in children, we discuss the interpretation of the measures of association and their implications.

Results

The results from data analysis highlighted major differences between estimated OR and PR. Results from simulation studies indicate an improved performance of delta method compared to bootstrap when there are small number of clusters.

Conclusion

We recommend the use of logistic model with random effects for analysis of clustered data. The choice of method to estimate confidence intervals for PR (delta or bootstrap method) should be based on study design.

Estimating relative risks for common outcome using PROC NLP

In cross-sectional or cohort studies with binary outcomes, it is biologically interpretable and of interest to estimate the relative risk or prevalence ratio, especially when the response rates are not rare. Several methods have been used to estimate the relative risk, among which the log-binomial models yield the maximum likelihood estimate (MLE) of the parameters. Because of restrictions on the parameter space, the log-binomial models often run into convergence problems. Some remedies, e.g., the Poisson and Cox regressions, have been proposed. However, these methods may give out-of-bound predicted response probabilities. In this paper, a new computation method using the SAS Nonlinear Programming (NLP) procedure is proposed to find the MLEs. The proposed NLP method was compared to the COPY method, a modified method to fit the log-binomial model. Issues in the implementation are discussed. For illustration, both methods were applied to data on the prevalence of microalbuminuria (micro-protein leakage into urine) for kidney disease patients from the Diabetes Control and Complications Trial. The sample SAS macro for calculating relative risk is provided in the appendix.

HIV prevention among travelers: why do men not use condoms when they engage in commercial sex overseas?

OBJECTIVES

We investigated factors associated with condom use among men patronizing female sex workers abroad and locally.

STUDY DESIGN

We conducted a survey on 372 local men attending the only public sexually transmitted infections clinic in Singapore between 2001 and 2003.

RESULTS

Condom use was higher among clients patronizing sex workers in Singapore than those patronizing sex workers abroad (87.5% vs. 54.4%, P<0.001). Condom use in both groups was associated with initiation of condom use by the sex workers (adjusted prevalence ratios: 1.67, 95% confidence interval: 1.11-2.49; 1.87, 1.21-2.90) but was not associated with clients' knowledge of disease, self-perceived risk, confidence in condom use, and dislike of condoms. Less sex workers abroad than in Singapore (32.7% vs. 75.6%, P<0.001) initiated condom use.

CONCLUSION

Lower condom use among Singaporean travelers abroad was determined by extrinsic factors, whereby sex workers abroad were less likely to initiate condom use rather than by clients' factors.

Willingness to donate blood samples for genetic research: a survey from a community in Singapore

Studies on the public's willingness to donate blood specimens for genetic research are few and are conducted mainly among Western countries. Little is known about the Asian community's willingness to participate in genetic research. A community-based survey was conducted on 548 adult Singaporeans to examine their willingness to donate blood samples for genetic research and its associated factors. The response rate was 70.3%. About 49.3% (95% CI, 45.1-53.5%) were willing to donate blood for genetic research. In the multivariable Cox regression analysis, willingness was significantly associated with belief in the benefits of genetic research; intention to participate in government studies; having no fear of pain, blood, injections, and needles; and non-concern about the loss of confidentiality. Reasons against donating blood were fear of pain, blood, injections, and needles (38.1%); no self-benefits (24.8%); fear of finding out about having a disease (22.3%); fear of discrimination (18.7%); and concerns about weakness (15.1%) and weight gain (9.4%). Public education programs to promote participation in genetic research should stress its benefits and address people's fears and concerns.

Effect measures in prevalence studies

There is still considerable confusion and debate about the appropriate methods for analyzing prevalence studies, and a number of recent papers have argued that prevalence ratios are the preferred method and that prevalence odds ratios should not be used. These arguments assert that the prevalence ratio is obviously the better measure and the odds ratio is "unintelligible." They have often been accompanied by demonstrations that when a disease is common the prevalence ratio and the prevalence odds ratio may differ substantially. However, this does not tell us which measure is the more valid to use. In fact, the prevalence odds ratio a) estimates the incidence rate ratio with fewer assumptions than are required for the prevalence ratio; b) can be estimated using the same methods as for the odds ratio in case-control studies, namely, the Mantel-Haenszel method and logistic regression; and c) provides practical, analytical, and theoretical consistency between analyses of a prevalence study and prevalence case-control analyses based on the same study population. For these reasons, the prevalence odds ratio will continue to be one of the standard methods for analyzing prevalence studies and prevalence case-control studies.

Long-term effects of condom promotion programmes for vaginal and oral sex on sexually transmitted infections among sex workers in Singapore

OBJECTIVES

To evaluate the long-term impact of condom promotion programmes for vaginal and oral sex among female brothel-based sex workers in Singapore.

DESIGN

A pre-test/post-test comparison group followed by a time series design was used to compare trends in condom use for vaginal sex and cervical gonorrhoea incidence from 1990 to 2002 across cross-sectional samples of sex workers before and after programme implementation in 1995. The subsequent condom promotion programme for oral sex was evaluated using the interrupted time series with a retrospective pre-test to post-test matched control group design.

METHODS

Sex workers completed a questionnaire before and 6 months after participation in educational sessions. Cervical and pharyngeal swabs were taken monthly for cultures for Neisseria gonorrhoeae.

RESULTS

Consistent condom use for vaginal sex increased significantly from < 45.0% before 1995 (pre-intervention period) to 95.1% in 2002, with a corresponding decline in cervical gonorrhoea incidence from > 30 to 2/1000 person-months. Adjustment for temporal changes in sociodemographic characteristics did not materially alter the trends. Consistent oral condom use increased significantly from < 50% before 1996 to 97.2% in 2002, with a corresponding decline in pharyngeal gonorrhoea from > 12 to 4.7/1000 person-months.

CONCLUSION

The interventions produced sustained high levels of condom use for vaginal and oral sex with corresponding declines in cervical and pharyngeal gonorrhoea incidence.

Alternatives for logistic regression in cross-sectional studies: an empirical comparison of models that directly estimate the prevalence ratio

BACKGROUND

Cross-sectional studies with binary outcomes analyzed by logistic regression are frequent in the epidemiological literature. However, the odds ratio can importantly overestimate the prevalence ratio, the measure of choice in these studies. Also, controlling for confounding is not equivalent for the two measures. In this paper we explore alternatives for modeling data of such studies with techniques that directly estimate the prevalence ratio.

METHODS

We compared Cox regression with constant time at risk, Poisson regression and log-binomial regression against the standard Mantel-Haenszel estimators. Models with robust variance estimators in Cox and Poisson regressions and variance corrected by the scale parameter in Poisson regression were also evaluated.

RESULTS

Three outcomes, from a cross-sectional study carried out in Pelotas, Brazil, with different levels of prevalence were explored: weight-for-age deficit (4%), asthma (31%) and mother in a paid job (52%). Unadjusted Cox/Poisson regression and Poisson regression with scale parameter adjusted by deviance performed worst in terms of interval estimates. Poisson regression with scale parameter adjusted by chi2 showed variable performance depending on the outcome prevalence. Cox/Poisson regression with robust variance, and log-binomial regression performed equally well when the model was correctly specified.

CONCLUSIONS

Cox or Poisson regression with robust variance and log-binomial regression provide correct estimates and are a better alternative for the analysis of cross-sectional studies with binary outcomes than logistic regression, since the prevalence ratio is more interpretable and easier to communicate to non-specialists than the odds ratio. However, precautions are needed to avoid estimation problems in specific situations.

Alternatives for logistic regression in cross-sectional studies: an empirical comparison of models that directly estimate the prevalence ratio

BACKGROUND

Cross-sectional studies with binary outcomes analyzed by logistic regression are frequent in the epidemiological literature. However, the odds ratio can importantly overestimate the prevalence ratio, the measure of choice in these studies. Also, controlling for confounding is not equivalent for the two measures. In this paper we explore alternatives for modeling data of such studies with techniques that directly estimate the prevalence ratio.

METHODS

We compared Cox regression with constant time at risk, Poisson regression and log-binomial regression against the standard Mantel-Haenszel estimators. Models with robust variance estimators in Cox and Poisson regressions and variance corrected by the scale parameter in Poisson regression were also evaluated.

RESULTS

Three outcomes, from a cross-sectional study carried out in Pelotas, Brazil, with different levels of prevalence were explored: weight-for-age deficit (4%), asthma (31%) and mother in a paid job (52%). Unadjusted Cox/Poisson regression and Poisson regression with scale parameter adjusted by deviance performed worst in terms of interval estimates. Poisson regression with scale parameter adjusted by chi2 showed variable performance depending on the outcome prevalence. Cox/Poisson regression with robust variance, and log-binomial regression performed equally well when the model was correctly specified.

CONCLUSIONS

Cox or Poisson regression with robust variance and log-binomial regression provide correct estimates and are a better alternative for the analysis of cross-sectional studies with binary outcomes than logistic regression, since the prevalence ratio is more interpretable and easier to communicate to non-specialists than the odds ratio. However, precautions are needed to avoid estimation problems in specific situations.

[Odds ratio or prevalence ratio? Their use in cross-sectional studies]

BACKGROUND

The most commonly used measures of association in cross-sectional studies are the odds ratio (OR) and the prevalence ratio (PR). Some cross-sectional epidemiologic studies describe their results as OR but use the definition of PR. The main aim of this study was to describe and compare different calculation methods for PR described in literature using two situations (prevalence < 20% and prevalence > 20%).

MATERIAL AND METHODS

A literature search was carried out to determine the most commonly used techniques for estimating the PR. The four most frequent methods were: 1) obtaining the OR using non-conditional logistic regression but using the correct definition; 2) using Breslow-Cox regression; 3) using a generalized linear model with logarithmic transformation and binomial family, and 4) using the conversion formula from OR into PR. The models found were replicated for both situations (prevalence less than 20% and greater than 20%) using real data from the 1994 Catalan Health Interview Survey.

RESULTS

When prevalence was low, no substantial differences were observed in either the estimators or standard errors obtained using the four procedures. When prevalence was high, differences were found between estimators and confidence intervals although all the measures maintained statistical significance.

CONCLUSION

All the methods have advantages and disadvantages. Individual researchers should decide which technique is the most appropriate for their data and should be consistent when using an estimator and interpreting it.

Promoting condoms for oral sex: impact on pharyngeal gonorrhea among female brothel-based sex workers

BACKGROUND

Low condom use for oral sex among female brothel-based sex workers in Singapore has led to a rise in pharyngeal gonorrhea.

GOAL

The goal of the study was to evaluate a program promoting the use of condoms for oral sex.

STUDY DESIGN

We used the time-series design to compare condom use and pharyngeal gonorrhea trends before and after program intervention in 1996 and the pretest-posttest matched control group design to determine the impact of brothel interventions on sex workers.

RESULTS

Consistent oral condom use increased significantly from 42.2% in 1996 to 89.9% in 2000, with a corresponding decline in pharyngeal gonorrhea (in comparison with no significant changes before intervention). Among sex workers in brothels with interventions there was a 10.8% absolute increase in condom use, compared with an 11.7% decrease in condom use in the control group. The gonorrhea incidence rate was also significantly much lower in the intervention group than in the control group (adjusted risk ratio: 0.22; 95% CI: 0.06-0.78).

CONCLUSION

The intervention increased oral condom use, with a decline in the incidence of pharyngeal gonorrhea.

Risk factors for work-related low back pain in the People's Republic of China

A critical review was conducted of studies of work-related low back pain in the People's Republic of China. The published literature in both the English and Chinese languages from 1983 to 1997 was reviewed for studies that permitted the calculation of prevalence ratios. Thirty-five papers were identified initially, and after quality inclusion/exclusion criteria were applied, 16 (14 in Chinese and two in English) were selected for more detailed review. Prevalence ratios were statistically elevated in all but two of the selected studies. Prevalence ratios for individual groups ranged from 2.0 to 8.5 for bending and twisting, 1.5 to 14.3 for static posture, 1.9 to 5.5 for whole-body vibration, and 2.6 to 9.4 for low-temperature exposure. The literature was limited by the absence of standardized and robust measures of low-back-pain outcomes and exposures and by the omission of fundamental details from research reports. Even with these limitations, the review findings suggest that three physical risk factors, all well known in the international literature, are associated with the prevalence of low back pain in the People's Republic of China.

Factors associated with condom use for oral sex among female brothel-based sex workers in Singapore

BACKGROUND AND OBJECTIVE

The prevalence of oral sex increased from 27.1% in 1992 to 81.1% in 1997, with a concomitant increase in pharyngeal gonorrhea, among female sex workers in Singapore. The extent of condom use for oral sex among them is unknown.

GOAL

To determine the prevalence of and factors associated with consistent condom use during oral sex.

STUDY DESIGN

A cross-sectional study of 225 women randomly selected from the surveillance scheme register of female brothel-based sex workers with a history of oral sex documented in their medical records.

RESULTS

Slightly more than half (56.9%) consistently used condoms for oral sex compared to 97% for vaginal sex. Condom use was significantly higher among middle than high class sex workers (adjusted rate ratio: 1.52, 95% CI: 1.01-2.29) and those with negotiation skills (adjusted rate ratio: 1.95, 95% CI: 1.32-2.07).

CONCLUSION

Sex workers should be taught skills to negotiate condom use for oral sex.

Sexually transmitted diseases and condom use among female freelance and brothel-based sex workers in Singapore

BACKGROUND AND OBJECTIVES

Most studies in Asia exclude freelance female sex workers because of difficulties in access and the illegality of their work. Data are lacking on their risk behaviors.

GOAL

To compare sexually transmitted disease (STD) rates, condom use, and health screening behavior between freelance and brothel-based sex workers in Singapore.

STUDY DESIGN

This is a cross-sectional survey of 111 free-lance sex workers arrested from November 1996 to March 1997 for illicit prostitution and 333 randomly selected brothel-based sex workers. All were tested for STDs.

RESULTS

STDs were significantly more prevalent among freelance than brothel-based sex workers (34.8% vs. 24.0%). Inconsistent condom use was significantly higher among freelance than brothel-based sex workers and was significantly associated with younger age, decreasing number of clients, and perception of non-condom use among peers.

CONCLUSION

Educational programs to promote condom use should target freelance sex workers and their clients.

Sociodemographic and lifestyle factors associated with constipation in an elderly Asian community

OBJECTIVE

We surveyed elderly individuals in an Asian community to determine the prevalence of constipation and its association with sociodemographic and lifestyle factors. This information will be used to plan a health promotion program for the elderly.

METHODS

A random sample of 2807 residents aged > or = 60 yr in Singapore were interviewed in their homes, using a standardized questionnaire. The response rate was 87.4% (n = 2454).

RESULTS

The overall age- and gender-adjusted prevalence rate of functional constipation was 11.6 per 100 persons (95% confidence interval [CI], 11.4-11.7). There were no gender or ethnic differences in constipation rates. Increased rates of constipation were significantly associated with advancing age. We found a significant dose-response relationship of increased constipation rates with decreased intake of rice, increased intake of Chinese tea, and number of chronic illnesses and medications, after controlling for potential confounders. Constipation was also significantly associated with lower intake of fruits and vegetables, but no dose-response gradient was seen.

CONCLUSIONS

Patients taking many medications should be monitored for constipation and given advice to avoid constipating factors. Further studies are needed to establish the causal-effect relationship of rice and Chinese tea with constipation.

Evaluation of the revised NIOSH lifting equation. A cross-sectional epidemiologic study

STUDY DESIGN

A cross-sectional study of the 1-year prevalence of low back pain was conducted in workers employed in manual lifting jobs.

OBJECTIVES

To provide epidemiologic data to determine the correlation between the prevalence of low back pain and exposure to manual lifting stressors, measured with the lifting index component of the revised lifting equation from the National Institute for Occupational Safety and Health (NIOSH).

SUMMARY OF BACKGROUND DATA

The NIOSH lifting equation has been proposed as a practical, yet valid tool for assessing the risks of low back pain caused by manual lifting. To date, however, there have been few studies in which the effectiveness of the equation to identify jobs with elevated rates of low back pain has been evaluated.

METHODS

Fifty jobs from four industrial sites were evaluated with the NIOSH lifting equation. A symptom and occupational history questionnaire was administered to 204 people employed in lifting jobs and 80 people employed in nonlifting jobs. Regression analysis was used to determine whether there was a correlation between the lifting index and reported low back pain.

RESULTS

As the lifting index increased from 1.0 to 3.0, the odds of low back pain increased, with a peak and statistically significant odds ratio occurring in the 2 < lifting index < or = 3 category (odds ratio = 2.45). For jobs with a lifting index higher than 3.0, however, the odds ratio was lower (odds ratio = 1.45).

CONCLUSIONS

Although low back pain is a common disorder, the lifting index appears be a useful indicator for determining the risk of low back pain caused by manual lifting.

Predictors of self-assessed work ability among subjects with recent-onset asthma

The objective of the study was to find predictors for work disability among adults with recent-onset asthma. The study was performed in a group of 332 subjects with recent-onset asthma. The predictors were ascertained by structured interviews, pulmonary function measurements, methacholine challenge tests and skin prick tests. Asthma severity was classified into mild, moderate or severe, based on the minimum medication required to maintain asthma control. Work ability was based on self-assessment by inquiring about the subjects' present work ability, expressed in percent. The self-reported work ability decreased significantly with increasing number of days off work, indicating that self-reported work ability reflects the actual work ability. The majority (56%) of the subjects reported 100% working ability. Among women, but not among men, working ability was negatively correlated (rs = -0.33) with age. Among subjects with PC20 < 16 mg ml-1 work ability increased with increasing PC20. There was no relation between FEV1, FVC and working ability. Asthma severity and current respiratory symptoms at the work place showed a significant negative relation with work ability. In a logistic regression model, when controlling for age, gender, smoking and weekly working hours, decreased work ability was associated with asthma severity, respiratory symptoms at the workplace and PC20 < or = 4 mg ml-1. In conclusion, the work ability was assessed as normal in most asthmatic subjects. Significant predictors for decreased work ability were asthma severity, workplace-associated respiratory symptoms and bronchial hyperresponsiveness. The results indicate that work ability among asthmatics could be improved by reducing the workplace-associated symptoms, either by reducing the exposure to triggers or by improving the asthma therapy.

Prevalence odds ratio or prevalence ratio in the analysis of cross sectional data: what is to be done?

OBJECTIVES

To review the appropriateness of the prevalence odds ratio (POR) and the prevalence ratio (PR) as effect measures in the analysis of cross sectional data and to evaluate different models for the multivariate estimation of the PR.

METHODS

A system of linear differential equations corresponding to a dynamic model of a cohort with a chronic disease was developed. At any point in time, a cross sectional analysis of the people then in the cohort provided a prevalence based measure of the effect of exposure on disease. This formed the basis for exploring the relations between the POR, the PR, and the incidence rate ratio (IRR). Examples illustrate relations for various IRRs, prevalences, and differential exodus rates. Multivariate point and interval estimation of the PR by logistic regression is illustrated and compared with the results from proportional hazards regression (PH) and generalised linear modelling (GLM).

RESULTS

The POR is difficult to interpret without making restrictive assumptions and the POR and PR may lead to different conclusions with regard to confounding and effect modification. The PR is always conservative relative to the IRR and, if PR > 1, the POR is always > PR. In a fixed cohort and with an adverse exposure, the POR is always > or = IRR, but in a dynamic cohort with sufficient underlying follow up the POR may overestimate or underestimate the IRR, depending on the duration of follow up. Logistic regression models provide point and interval estimates of the PR (and POR) but may be intractable in the presence of many covariates. Proportional hazards and generalised linear models provide statistical methods directed specifically at the PR, but the interval estimation in the case of PH is conservative and the GLM procedure may require constrained estimation.

CONCLUSIONS

The PR is conservative, consistent, and interpretable relative to the IRR and should be used in preference to the POR. Multivariate estimation of the PR should be executed by means of generalised linear models or, conservatively, by proportional hazards regression.

Estimating the incidence rate ratio in cross-sectional studies using a simple alternative to logistic regression

PURPOSE

Logistic regression is often used for the analysis of cross-sectional studies, and prevalence odds and odds ratios are obtained. Other methods have been proposed for estimating prevalence ratios. An alternative regression method is also available for estimating rate ratios. Its application to cross-sectional studies is discussed.

METHODS

When dealing with chronic conditions, it is possible to model binomial data using the complementary log-log link function log(-log(1-pi)), where pi is the prevalence, an option available on many statistical software packages. In effect, these are models for the disease incidence rate lambda, which is assumed to be constant over the underlying follow-up period t. This approach is based on the well-known relationship 1-pi-exp(-lambda t). The cumulative effect of age on prevalence (effectively "time of follow up") can be accounted for in the model, by specifying it as an offset.

RESULTS

The regression coefficients associated with the covariates included in the model estimate rate ratios, rather than odds or prevalence ratios. The method is applied to the analysis of the prevalence of respiratory symptoms in 4395 children aged 7-9 years who are residents of Huddersfield (northern England), surveyed in the framework of the SAVIAH (Small Area Variations of Air Quality and Health) study.

CONCLUSIONS

By considering saturated models including only sex as a covariate, direct comparison of crude and fitted parameters (odds, prevalence, and rate ratios) shows that, for short follow-up periods, the complementary log-log model is a valid alternative to logistic regression. More complex models including other covariates are also discussed.

Musculoskeletal symptoms and job strain among nursing personnel: a study over a three year period

OBJECTIVES

To examine the variation of symptoms from the neck, shoulders, and back over a three year period among female nursing personnel and the relation between job strain and musculoskeletal symptoms.

METHODS

At a county hospital the female nursing personnel answered a questionnaire at baseline and then once a year over a period of three years. There were 565, 553, 562, and 419 subjects who answered the questionnaire at the first, second, third, and fourth survey, respectively. Of the study group, 285 nursing personnel answered the questionnaire on four occasions. Ongoing symptoms of the neck, shoulders, and back were assessed by means of a 10 point (0-9) scale with the verbal end points "no symptoms" and "very intense symptoms." Cases were defined as nursing personnel reporting ongoing symptoms, score > 6, from at least one of the body regions. For assessments of job strain, a Swedish version of Karasek and Theorell's model was used.

RESULTS

Of the 285 subjects, 13% were defined as cases at all four assessments, and 46% varied between cases and not cases during the study period. In the repeated cross sectional surveys the estimated rate ratio (RR) for being a case was between 1.1 and 1.5 when comparing the group with job strain and the group without job strain. For the combination of job strain and perceived high physical exertion the estimated RR was between 1.5 and 2.1. When the potential risk factors were assessed one, two, or three years before the assessment of symptoms the estimated RR for becoming a case was between 1.4 and 2.2 when comparing the group with job strain and the group without job strain.

CONCLUSION

Almost half of the healthcare workers varied between being a case and not, over a three year period. The analysis indicated that job strain is a risk factor for musculoskeletal symptoms and that the risk is higher when it is combined with perceived high physical exertion.

Infant walker use, injuries, and motor development

OBJECTIVES

To study the impact of infant walker use on motor development and injuries.

POPULATION

One hundred and eighty five parents or primary care givers who attended a Singapore government polyclinic from September 1993 to February 1994, with their infants between 7 to 10 months, for a developmental assessment session.

SETTING

A government polyclinic in Singapore.

METHODS

The parent or primary care giver answered questions pertaining to infant walker use and injuries attributed to its use. Each infant was then given the Singapore modified version of the Denver Developmental Screening Test (DDST-S), along with a full clinical examination; both testers were blinded to walker use.

RESULTS

One hundred and sixty seven (90%) of 185 infants used walkers regularly, and 21 (12.5%) of the users had one or more injuries. Most injuries were minor, such as bruises and swellings on the head, forehead, face, and cheeks. None of the children who did not use walkers showed any abnormal DDST-S results whereas 18 (10.8%) of the 167 walker users had either abnormal or questionable DDST-S results.

CONCLUSIONS

12.5% of walker users had one or more injuries and walker use may also delay the child's motor development. These findings will help the physician or nurse in primary care settings to advise parents about the potential hazards of walker use.

[Ratio of proportions and the use of the delta method for confidence intervals in logistic regression]

OBJECTIVE

To present an application of logistic regression modelling to estimate ratios of proportions, such as prevalence ratio or relative risk, and the Delta Method to estimate confidence intervals.

METHOD

The Delta Method was used because it is appropriate for the estimation of variance of non-linear functions of random variables. The method is based on Taylor's series expansion and provides a good approximation of variance estimates. A computer program, utilizing the matrix module of SAS, was developed to compute the variance estimates. A practical demonstration is presented with data from a cross-sectional study carried out on a sample of 611 women, to test the hypothesis that the lack of housework sharing is associated with high scores of psychological symptoms as measured by a validated questionnaire.

RESULTS

Crude and adjusted prevalence ratio estimated by logistic regression were similar to those estimated by tabular analysis. Also, ranges of the confidence intervals of the prevalence ratio according to the Delta Method were nearly equal to those obtained by the Mantel-Haenszel approach.

CONCLUSIONS

The results give support to the use of the Delta Method for the estimation of confidence intervals for ratios of proportions. The method should be seen as an alternative for situations in which the need to control a large number of potential confounders limits the use of stratified analysis.

Self-reported physical exertion in geriatric care. A risk indicator for low back symptoms?

STUDY DESIGN

The study group consisted of 131 female nursing aides who took part in an intervention program with physical training or education. Assessments were performed before the intervention program and after 6 months. At follow-up evaluation, 91 nursing aides remained in the study.

OBJECTIVES

To examine if perceived physical exertion was a risk indicator for low back symptoms, and to examine the relationship between perceived physical exertion, aerobic capacity, back endurance, psychological demands, and job control.

SUMMARY OF BACKGROUND DATA

Perceived physical exertion frequently is assessed in epidemiologic studies concerning low back symptoms. More information about the relationship between perceived exertion, other potential risk indicators, and symptoms may provide opportunities for effective prevention of symptoms.

METHODS

Assessments were obtained by questionnaires and physical capacity tests.

RESULTS

The nursing aides who reported high physical exertion and were 45 years of age or older were at greater risk in the follow-up period for reporting new symptoms, continued symptoms with the same intensity, or more intense symptoms from the low back (rate ratio, 3.01; 95% confidence interval, 1.1-8.2). The exposure variable correlated most strongly (r = 0.4) with perceived physical exertion was psychological demands.

CONCLUSIONS

The results indicated being aged 45 years or older, combined with high perceived physical exertion, was a risk indicator for low back symptoms. A relationship between perceived physical exertion and psychological demands was observed, but there was no influence of physical capacity on perceived physical exertion.