Characteristics of non-participants and reasons for non-participation in a population survey in Kin-Hu, Kinmen

Asking informed consent may lead to significant participation bias and suboptimal cardiovascular risk management in learning healthcare systems

BACKGROUND

The Utrecht Cardiovascular Cohort - CardioVascular Risk Management (UCC-CVRM) was set up as a learning healthcare system (LHS), aiming at guideline based cardiovascular risk factor measurement in all patients in routine clinical care. However, not all patients provided informed consent, which may lead to participation bias. We aimed to study participation bias in a LHS by assessing differences in and completeness of cardiovascular risk management (CVRM) indicators in electronic health records (EHRs) of consenting, non-consenting, and non-responding patients, using the UCC-CVRM as an example.

METHODS

All patients visiting the University Medical Center Utrecht for first time evaluation of a(n) (a)symptomatic vascular disease or condition were invited to participate. Routine care data was collected in the EHR and an informed consent was asked. Differences in patient characteristics were compared between consent groups. We performed multivariable logistic regression to identify determinants of non-consent. We used multinomial regression for an exploratory analysis for the determinants of non-response. Presence of CVRM indicators were compared between consent groups. A waiver (19/641) was obtained from our ethics committee.

RESULTS

Out of 5730 patients invited, 2378 were consenting, 1907 non-consenting, and 1445 non-responding. Non-consent was related to young and old age, lower education level, lower BMI, physical activity and haemoglobin levels, higher heartrate, cardiovascular disease history and absence of proteinuria. Non-response increased with young and old age, higher education level, physical activity, HbA1c and decreased with lower levels of haemoglobin, BMI, and systolic blood pressure. Presence of CVRM indicators was 5-30% lower in non-consenting patients and even lower in non-responding patients, compared to consenting patients. Non-consent and non-response varied across specialisms.

CONCLUSIONS

A traditional informed consent procedure in a LHS may lead to participation bias and potentially to suboptimal CVRM, which is detrimental for feedback on findings in a LHS. This underlines the importance of reassessing the informed consent procedure in a LHS.

Improving retention of community-recruited participants in HIV prevention research through Saturday household visits; findings from the HPTN 071 (PopART) study in South Africa

BACKGROUND

Identifying successful strategies to improve participant retention in longitudinal studies remains a challenge. In this study we evaluated whether non-traditional fieldworker shifts (after hours during the week and weekends) enhanced participant retention when compared to retention during traditional weekday shifts in the HPTN 071 (PopART) population cohort (PC).

METHODS

HPTN 071 (PopART) PC participants were recruited and followed up in their homes on an annual basis by research fieldworkers over a 3-4 year period. The average number of successful follow-up visits, where a PC participant was found and retained in the study, was calculated for each of 3 visit schedules (early weekday shift, late weekday shift, and Saturday shift), and standardized to account for variation in fieldwork shift duration. We used one-way univariate analysis of variance (ANOVA) to describe differences in mean-successful visits and 95% confidence intervals between the shift types.

RESULTS

Data on 16 651 successful visits were included. Successful visit rates were higher when conducting Saturday visits (14.0; 95% CI: 11.3-16.6) compared to both regular (4.5; 95% CI: 3.7-5.3) and late weekday shifts (5.3; 95% CI: 4.7-5.8) overall and in all subgroup analyses (P<0.001). The successful visit rate was higher amongst women than men were during all shift types (3.2 vs. 1.3, p<0.001). Successful visit rates by shift type did not differ significantly by age, over time, by PC round or by community triplet.

CONCLUSION

The number of people living with HIV continues to increase annually. High quality evidence from longitudinal studies remains critical for evaluating HIV prevention and treatment strategies. This study showed a significant benefit on participant retention through introduction of Saturday shifts for home visits and these data can make an important contribution to the emerging body of evidence for improving retention in longitudinal research.

TRIAL REGISTRATION

PopART was approved by the Stellenbosch University Health Research Ethics Committees (N12/11/074), London School of Hygiene and Tropical Medicine (6326) ethics committee and the Division of AIDS (DAIDS) (Protocol ID 11865). PopART was registered with ClinicalTrials.gov (registration number NCT01900977 ).

Sociodemographic Factors Influenced Response to the 2015 National Nutrition Survey on Preschool Children: Results From Linkage With the Comprehensive Survey of Living Conditions

BACKGROUND

The National Nutrition Survey on Preschool Children, Japan (NNSPC) provides fundamental information for policy making for child nutrition. However, the response rate and background characteristics of subjects are unclear. Here, we examined response rate and sociodemographic factors related with response to the survey and evaluated the magnitude of bias due to selective response in the survey estimates of the NNSPC.

METHODS

This study was based on two national surveys conducted in 2015: the NNSPC and the Comprehensive Survey of Living Conditions (CSLC). Because potential survey participants of the NNSPC were children aged <6 years and their households that answered the CSLC, we examined response rates and respondent characteristics by linking the data of the NNSPC and CSLC. Multiple logistic regression analysis was used to identify sociodemographic factors associated with response. Potential bias caused by non-response in the survey estimates was examined after considering missingness through multiple imputation.

RESULTS

Among the 5,343 children who participated in the CSLC, 3,426 children responded to the NNSPC (response rate = 64.1%). Variables associated with response were living in a smaller city, a large number of children, three-generation family structure, older maternal age, and a non-working mother. The prevalence of overweight was underestimated by 20%, but the bias for almost all variables examined was small.

CONCLUSIONS

Response to the survey varied by sociodemographic characteristics. Some biases, mostly small, were seen in survey estimates of the 2015 NNSPC. Further insight into the effect of selective response is important to assess associations between variables more precisely.

Measuring quality of life of primary antibody deficiency patients using a disease-specific health-related quality of life questionnaire for common variable immunodeficiency (CVID_QoL)

Background

Common variable immunodeficiency (CVID) and other primary antibody deficiencies (PAD) are a heterogeneous group of > 300 congenital disorders affecting the immune system. Until recently, efforts to measure health-related quality of life (QoL) in PAD patients have utilised generic QoL tools and disease-specific tools for other conditions. Still, the full impact of the disease is probably not understood. We evaluated the performance of the CVID_QoL, a novel disease-specific QoL instrument for adults with CVID, on Norwegian PAD patients and compared the results to those of the generic WHOQOL-BREF.

Methods

Respondents were recruited through the Norwegian Centre for Rare Disorders’ patient database. Included patients fulfilled the following criteria (all three): 1.) Age ≥18 years, 2.) a PAD diagnosis, 3.) currently on immunoglobulin therapy. The CVID_QoL is a 32-item questionnaire. Global CVID_QoL scores were compared between Norwegian PAD patients and Italian CVID patients.

Results

In total, 83 PAD patients filled out the CVID_QoL, 63% had CVID, 76% were females. 32 patients filled out the WHOQOL-BREF. Feasibility was high (<1% missing). Internal consistency for the emotional- (Cronbach’s α-value = 0.91) and relational functioning (α =  0.77) subscales was high, but questionable for the gastrointestinal and skin symptoms subscale (α =  0.66). Convergent validity varied from weak to strong (range 0.3–0.8). Floor and ceiling effects were present.

Conclusions

Although many disease-specific characteristics are probably shared with CVID and other PAD, the CVID_QoL captures some, but not all, dimensions of PAD patients’ QoL. More evaluations of the CVID_QoL’s performance in different contexts are needed.

Electronic supplementary material

The online version of this article (10.1186/s41687-019-0101-x) contains supplementary material, which is available to authorized users.

Representativity of a postal public health questionnaire survey in Sweden, with special reference to ethnic differences in participation

Aim: Non-participation in health surveys is a common phenomenon. When differences between participants and non-participants are considerable, the external validity of the sample survey may decrease and false conclusions might be drawn about the health status of the population. For this reason, the authors aimed to investigate the representativity of a postal questionnaire survey performed in the county of Scania, Sweden, in 1999—2000. The survey, which was based on an 18- to 80-year-old population sample, had a 58% response rate (n = 13 604). Methods: For some variables, the information obtained using the questionnaire was compared with information obtained from a population register that covers all the population in the county (for the 18- to 80-year-old group, n = 850 476). The population register includes, among other data, information on age, gender, educational level, country of birth, and healthcare expenditure. Results: Men, individuals with a low level of education, and immigrants were under-represented in the survey. However, except for immigrants, the under-representation was not large. Among immigrants, particularly those born in former Yugoslavia, the Arabic-speaking countries, and Poland were very significantly under-represented in the study. By contrast, immigrants born in other Nordic countries had responded to almost the same extent as respondents born in Sweden. The survey sample had about the same healthcare utilization costs as did the general population. Conclusions: In summary, the ``Health Survey for Scania, 2000'' seems largely representative of the total Scanian population. A major concern, however, is the under-representation of the immigrant population.

Baseline participation in a health examination survey of the population 65 years and older: who is missed and why?

Background

Public health monitoring depends on valid health and disability estimates in the population 65+ years. This is hampered by high non-participation rates in this age group. There is limited insight into size and direction of potential baseline selection bias.

Methods

We analyzed baseline non-participation in a register-based random sample of 1481 inner-city residents 65+ years, invited to a health examination survey according to demographics available for the entire sample, self-report information as available and reasons for non-participation. One year after recruitment, non-responders were revisited to assess their reasons.

Results

Five groups defined by participation status were differentiated: participants (N = 299), persons who had died or moved (N = 173), those who declined participation, but answered a short questionnaire (N = 384), those who declined participation and the short questionnaire (N = 324), and non-responders (N = 301). The results confirm substantial baseline selection bias with significant underrepresentation of persons 85+ years, persons in residential care or from disadvantaged neighborhoods, with lower education, foreign citizenship, or lower health-related quality of life. Finally, reasons for non-participation could be identified for 78 % of all non-participants, including 183 non-responders.

Conclusion

A diversity in health problems and barriers to participation exists among non-participants. Innovative study designs are needed for public health monitoring in aging populations.

Sex-differences in reasons for non-participation at recruitment: Geelong Osteoporosis Study

Background

Understanding reasons for non-participation in health studies can help guide recruitment strategies and inform researchers about potential sources of bias in their study sample. Whilst there is a paucity of literature regarding this issue, it remains highly plausible that men and women may have varied reasons for declining an invitation to participate in research. We aimed to investigate sex-differences in the reasons for non-participation at baseline of the Geelong Osteoporosis Study (GOS).

Methods

The GOS, a prospective cohort study, randomly recruited men and women aged 20 years and over from a region in south-eastern Australia using Commonwealth electoral rolls (2001–06 and 1993–97, respectively). Reasons for non-participation (n=1,200) were documented during the two recruitment periods. We used the Pearson’s chi squared test to explore differences in the reasons for non-participation between men and women.

Results

Non-participation in the male cohort was greater than in the female cohort (32.9% vs. 22.9%; p<0.001). Overall, there were sex-differences in the reasons provided for non-participation (p<0.001); apparent differences related to time constraints (men 26.3% vs. women 10.4%), frailty/inability to cope with or understand the study (men 18.7% vs. women 30.6%), and reluctance over medical testing (men 1.1% vs women 9.9%). No sex-differences were observed for non-participation related to personal reason/disinterest, and language- or travel-related reasons.

Conclusions

Improving participation rates in epidemiological studies may require different recruitment strategies for men and women in order to address sex-specific concerns about participating in research.

[Analysis of selection bias in the pilot study of a longitudinal study on aging in Spain]

OBJECTIVES

To demonstrate that selection of a probabilistic sample at a national level for a study of aging in Spain is subject to selection bias. To quantify the losses produced after each phase of the administration of a questionnaire.

METHODS

We performed a cross-sectional study of the Spanish community-dwelling population aged 50 years or older between 2010 and 2011. Through multivariate logistic regressions, the characteristics of the census tract of the patients' residence were compared between those who agreed (n = 5,813) or refused (n = 7,023) to be included in the sampling frame and between those who agreed (n = 1,677) or refused (n = 2,875) to participate in the study. The individual characteristics of persons who responded (n = 1,398) or refused to respond (n = 346) to a face-to-face questionnaire administered after a telephone interview were also compared. In addition, the reasons for refusal were studied.

RESULTS

The most frequent specific reasons for refusing to be included in the sampling frame or to participate in the study were poor health and disability (14.4% and 27.9%, respectively). In both cases, refusal was more frequent in the census tracts of districts with a lower socioeconomic level or those located in Catalonia, Guipúzcoa or Biscay. Individuals older than 81 participated less frequently in the face-to-face questionnaire. Between 8.6% and 18.4% of participants were lost at each stage of information retrieval.

CONCLUSION

Probabilistic sampling in sampling points chosen by the researchers would allow more resources to be devoted to increasing response rates among the groups who are less likely to participate. Questions should be concentrated in only one shorter questionnaire, administered before blood extraction.

Adjusting a cancer mortality-prediction model for disease status-related eligibility criteria

Background

Volunteering participants in disease studies tend to be healthier than the general population partially due to specific enrollment criteria. Using modeling to accurately predict outcomes of cohort studies enrolling volunteers requires adjusting for the bias introduced in this way. Here we propose a new method to account for the effect of a specific form of healthy volunteer bias resulting from imposing disease status-related eligibility criteria, on disease-specific mortality, by explicitly modeling the length of the time interval between the moment when the subject becomes ineligible for the study, and the outcome.

Methods

Using survival time data from 1190 newly diagnosed lung cancer patients at MD Anderson Cancer Center, we model the time from clinical lung cancer diagnosis to death using an exponential distribution to approximate the length of this interval for a study where lung cancer death serves as the outcome. Incorporating this interval into our previously developed lung cancer risk model, we adjust for the effect of disease status-related eligibility criteria in predicting the number of lung cancer deaths in the control arm of CARET. The effect of the adjustment using the MD Anderson-derived approximation is compared to that based on SEER data.

Results

Using the adjustment developed in conjunction with our existing lung cancer model, we are able to accurately predict the number of lung cancer deaths observed in the control arm of CARET.

Conclusions

The resulting adjustment was accurate in predicting the lower rates of disease observed in the early years while still maintaining reasonable prediction ability in the later years of the trial. This method could be used to adjust for, or predict the duration and relative effect of any possible biases related to disease-specific eligibility criteria in modeling studies of volunteer-based cohorts.

Attrition in a panel study of people with environmental exposures: new insights about the impact of race, sex, and number of children in the household

This study examines attrition in a panel survey. Each member of the panel was selected because of their documented exposure to long-term, low levels of hazardous substances in their residential water. In addition, each was informed of their exposure at the time of baseline contact. The analytic approach involves examining the interactive effect of race and sex, as well as the additive effect of household characteristics on the propensity to stay. The data are derived from the National Exposure Registry, which is a large-scale, longitudinal health survey. This study finds that compared with white males, non-white males are more likely to attrite and white females are more likely to stay in the study. In addition, the propensity to stay is affected by the number of children in the household. These findings have implications for field procedures that may involve the selective targeting at baseline of those subgroups with a greater propensity to attrite.

Non-response to baseline, non-response to follow-up and mortality in the Whitehall II cohort

BACKGROUND

Little is known about the associations between non-response to follow-up surveys and mortality, or differences in these associations by socioeconomic position in studies with repeat data collections.

METHODS

The Whitehall II study of socioeconomic inequalities in health provided response status from five data collection surveys; Phase 1 (1985-88, n = 10 308), Phase 5 (1997-99, n = 6533), and all-cause mortality to 2006. Odd-numbered phases included a medical examination in addition to a questionnaire.

RESULTS

Non-response to baseline and to follow-up phases that included a medical examination was associated with a doubling of the mortality hazard in analyses adjusted for age and sex. Compared with complete responders, responders who missed one or more phases, but completed the last possible phase before they died, had a 38% excess risk of mortality. However, those who missed one or more phases including the last possible phase before death had an excess risk of 127%. There was no evidence that these associations differed by socioeconomic position.

CONCLUSION

In studies with repeat data collections, non-response to follow-up is associated with the same doubling of the mortality risk as non-response to baseline; an association that is not modified by socioeconomic position.

Adolescent survey non-response and later risk of death. A prospective cohort study of 78,609 persons with 11-year follow-up

Background

Non-response in survey studies is a growing problem and, being usually selective, it leads to under- or overestimation of health outcomes in the follow-up. We followed both respondents and non-respondents by registry linkage to determine whether there is a risk of death, related to non-response at baseline.

Methods

Sample data of biennial surveys to 12-18-year-old Finns in 1979–1997 were linked with national death registry up to 2001. The number of respondents was 62 528 (79.6%) and non-respondents 16 081 (20.4%). The average follow-up was 11.1 years, totalling 876 400 person-years. The risk of death between non-respondents and respondents was estimated by hazard ratios (HR).

Results

The number of deaths per 100 000 person-years were 229 in non-respondents and 447 in respondents (HR 2.0, 95% CI: 1.5–2.6). The hazard ratios of death were for intoxication 3.2 (95% CI: 1.9–5.4), for disease 3.1 (95% CI: 2.2–4.1), for violence-related injury 2.0 (95% CI: 1.5–2.6) and for unintentional injury 1.8 (95% CI: 1.3–2.4) in non-respondents vs. respondents. The association between non-response and death increased with age at baseline, and the increase persisted after the age of 25.

Conclusion

Our study demonstrated significantly increased rates of death among adolescent non-respondents in a follow-up. The highest hazard ratios were seen in disease- and violence-related deaths. The death rate varied between respondents and non-respondents by death type. Increased rates of death persisted beyond the age of 25.

Interrelationship Between Insulin Resistance and Menopause on the Metabolic Syndrome and Its Individual Component Among Nondiabetic Women in the Kinmen Study

BACKGROUND

The literature to date is not clear as to whether any interactive effect exists between insulin resistance and menopause on the metabolic syndrome and its individual components. We explored this issue in 4107 homogeneous, nondiabetic Chinese women in the Kinmen Study.

METHODS

Overnight fasting blood samples were drawn for glucose, insulin, lipid, and other biochemical measurements. Demographic and clinical variables including body mass index, waist circumference, and blood pressure were measured and documented during face-to-face interviews with structured questionnaires. Menstrual history was used to define menopause as the absence of menses for 12 consecutive months.

RESULTS

Approximately 16% of premenopausal women (390/2423) were insulin-resistant. After adjustment for age, body mass index, lifestyle, and diet, both menopause and insulin resistance were independently and significantly correlated with metabolic syndrome. For each component of the metabolic syndrome, besides the main effect, the interaction (insulin resistance x menopause) had significant correlation with systolic blood pressure, diastolic blood pressure, and waist circumference.

CONCLUSIONS

Both insulin resistance and menopause have significant effects on metabolic syndrome independent of age and obesity. In premenopausal and nondiabetic women, various degrees of insulin resistance exist. The synergistic contribution of insulin resistance and menopause to components of the metabolic syndrome were observed with systolic blood pressure, diastolic blood pressure, and waist circumference. This requires further study.

Community-based study on summer-winter differences of component of metabolic syndrome in Kinmen, Taiwan

BACKGROUND

A community-based study was conducted to investigate summer-winter differences of component of metabolic syndrome in Kinmen, Taiwan.

METHODS

A total of 8251 residents aged 40 and over were enrolled in the mass survey in Kinmen. They were investigated while on summer (July and August) and winter vacation (January and February) during 2000-2003. Demographics, physical examination findings, lifestyle variables and biochemical data were collected.

RESULTS

After controlling for age, body mass index, diet, lifestyle and other risk factors for component of metabolic syndrome, there were independent and significant relationships between summer-winter difference and component of metabolic syndrome. Winter season was positively correlated with blood pressure, fasting plasma glucose level, high-density lipoprotein-cholesterol (HDL-C) and waist circumference, but was negatively associated with fasting triglycerides and metabolic syndrome.

CONCLUSIONS

Summer season is positively associated with hypertriglyceridemia, low HDL-C and metabolic syndrome. These findings imply that cross-sectional, experimental and cohort studies of component of metabolic syndrome or metabolic syndrome should take season into account as possible confounding effects.

Comparison of smoking, drinking, and marijuana use between students present or absent on the day of a school-based survey

The aim of this population-based survey was to compare the prevalence of selected risk behaviors between students present or absent on the day of a school-based survey. The study population was a representative sample of all students of secondary schools in the Seychelles (Indian Ocean). Students absent on the day of the survey were traced and requested to complete the same self-administered questionnaire as did present students. Self-reported consumption of cigarettes, alcohol, and marijuana were measured. Of the sample of 1453 eligible students aged 11 to 17 years, 1321 "present students" completed the survey (90.9% participation), 11 refused to answer all questions, and 121 were not present at school. We could trace 105 of the 121 students not present at school on the survey day ("absent students"), and all of them completed the questionnaire over the next 4 weeks. The prevalence of risk behaviors was significantly higher in absent than present students for current smoking and drinking. Inclusion of data from the absent students resulted in a relative increase in the prevalence of the considered behaviors by 3% to 8% as compared to data based on present students only. In conclusion, the prevalence of risk behaviors was higher in absent than present students. Adjusting for data of absent students increased the prevalence estimates in the base population.

Lower prevalence of heart disease but higher mortality risk during follow-up was found among nonrespondents to a cohort study

OBJECTIVE

The primary aim was to assess the association between response behavior and health status at baseline, and survival in a 5-year follow-up period. A secondary aim was to assess whether reasons for nonresponse were associated with health status at baseline.

STUDY DESIGN AND SETTING

Data came from a prospective study cohort consisting of 31,349 men and women aged 45-70 years. Objective retrospective and prospective health information derived from general practitioner registries was available for both respondents and nonrespondents.

RESULTS

Results show that among respondents coronary heart disease was more prevalent. Compared with respondents, noncontacts had a higher mortality risk during follow-up. Refusals had hypercholesterolemia more often than did noncontacts, and coronary heart disease or diabetes mellitus less often.

CONCLUSION

The paradoxical results that respondents are less healthy at baseline but prospectively have a lower mortality risk may point to a selection effect indicating that the 'worried ill' are more inclined to participate. This effect could imply that observed relationships between risk factors or behaviors and outcomes in cohort studies may be attenuated.

Differences in higher-level functional capacity between participants and non-participants in health checkups among the elderly

The present study was conducted to characterize the lifestyles and health status of non-participants and to investigate whether diminished higher-level functional capacity may cause selection bias in non-compulsory mass health screening for the elderly. Using a self-administered questionnaire for evaluating the Tokyo Metropolitan Institute of Gerontology Index of Competence (TMIG Index of Competence) which consists of three sublevels, namely, instrumental self-maintenance, intellectual activity and social role, we conducted a survey of 1543 (mean age, 64.9+/-12.5 years, 677 males and 866 females) out of all the 1701 individuals over the age of 40 residing in a village where mass health screening is conducted annually. The mean TMIG Index of Competence score was the highest in Group V (composed of 434 individuals who participated in the mass health screening conducted by the village), followed, in that order, by the score in Group W (composed of 531 individuals who had undergone a health checkup organized at their workplaces or by their family physicians, but not the one conducted by the village, during the previous year) and that in Group N (composed of 578 individuals who had not undergone any health checkup during the previous year). Group N showed a significantly lower mean TMIG Index of Competence score than Groups V and W. In regard to the scores for the sublevels of the index, Group N had a significantly lower percentage of subjects, both men and women, with perfect scores than Group V for all the sublevels, and also a significantly lower percentage of subjects with a perfect score for the intellectual activity than Group W. However, there were no significant differences in the percentages of subjects habituated to exercise, drinking or smoking among the three groups. Thus, special attention may need to be paid to selection bias in mass health screenings caused by differences in the higher-level functional capacity.

Characteristics of non-response in the Danish Health Interview Surveys, 1987–1994

BACKGROUND

The types and quantity of non-response in surveys influence the extent to which the results may be generalized. This study analysed trends in non-response in the Danish Health Interview Surveys from 1987 to 1994 and used the National Patient Registry to assess whether non-response biased the estimated population prevalence of morbidity when solely based on responders.

METHODS

The data were for the 23,096 adults sampled for the Danish Health Interview Surveys in 1987, 1991 and 1994. All were followed using the National Patient Registry to obtain such information as hospital admissions.

RESULTS

Non-response increased from 20.0% in 1987 to 22.6% in 1994. Four combinations of background variables characterized the non-response: gender and age; gender and civil status; county of residence and age; survey year and age. Non-respondents and respondents had identical gender- and age-standardized hospital admission rates for approximately 5 years before and 2 years after data collection, but non-respondents had a significantly higher rate immediately before and during data collection. Admissions rates were analysed according to reasons for non-response. Refusers had a lower admission rate than respondents before data collection but similar during and after data collection. The rate was higher during the whole period among ill or disabled non-respondents. Among people who could not be contacted during the data collection period a higher admission rate was only found immediately before and during data collection.

CONCLUSIONS

Although admission rates differed between respondents and non-respondents these differences were too small to bias the estimated population prevalence of morbidity when solely based on respondents.

A cross-sectional analysis demonstrated the healthy volunteer effect in smokers

OBJECTIVE

This cross-sectional descriptive analysis sought to determine if a healthy volunteer effect can be demonstrated among smokers selected to participate in a dietary intervention trial.

STUDY DESIGN AND SETTING

Body mass index (BMI), body fat, physical activity, dietary intake, and plasma concentration of antioxidant nutrients and carotenoids were assessed cross-sectionally, at the time of enrollment into a dietary intervention trial, among 136 adult smokers.

RESULTS

Mean BMI was below national age- and gender-specific averages as was prevalence of overweight and obesity. Physical activity was reported to average 15.4 h/wk. Compared with other sample populations of smokers, our smokers reported lower total fat and cholesterol intakes, higher vitamin C and beta-carotene intakes, and generally equal vitamin E intakes. Plasma ascorbic acid, alpha-tocopherol, alpha- and beta-carotene, and beta-cryptoxanthin concentrations were higher than those of smokers surveyed by NHANES III.

CONCLUSION

These findings suggest that a "healthy volunteer effect" can be described among adult smokers. Future dietary intervention trials among smokers should cautiously estimate sample size because smokers electing to participate may report healthier dietary patterns than other smokers. Screening criteria regarding baseline micronutrient status of smokers should be evaluated given that intervention effects may be dependent on overall health status.

Long-term health sequelae following E. coli and campylobacter contamination of municipal water. Population sampling and assessing non-participation biases

BACKGROUND

Following bacterial contamination of a municipal water system in the rural town of Walkerton, Ontario, over 2,300 cases of acute gastroenteritis were documented. The Walkerton Health Study is currently underway to assess for long-term health sequelae among consenting inhabitants of Walkerton, related to the original outbreak. We explored whether the association between the acute exposure and preliminary long-term health outcomes may have been biased through differences between early- and late-recruited study participants.

METHODS

Using multiple data sources, including the 1996 and 2001 Canadian Census, and records from the Regional Health Unit, hospital and Walkerton Health Study, we determined both sample representativeness and the anticipated effects of intensifying study participant recruitment. Selection bias was assessed by examining for differences between initial and late participants, and their subsequent risk of having hypertension, proteinuria and reduced renal clearance.

RESULTS

Of the 4,315 participants, 2,756 were permanent residents of Walkerton, representing 55% of the town's total population. The sample was demographically similar to the population of interest, although statistically women were more likely to participate than men (55% of sample were women compared to 52% of population, p<0.01), and the proportion of both young and very elderly adults was smaller than expected (13% of sample were > or = 65 years of age compared to 18% of population, p<0.01). Comparing the initial 3,959 participants to the 356 persons additionally recruited with substantial effort, the latter were more likely to be free of symptoms during the outbreak (21% vs. 7%, p<0.001), but were otherwise similar in terms of age, sex, the use of medical care resources and underlying health state predating the outbreak. The risk of long-term hypertension or renal sequelae did not significantly differ between initial and late study recruits.

CONCLUSIONS

Participants in the Walkerton Health Study represent the population of interest, and comprise those who were acutely ill during the infected water outbreak. The available study sample should provide reasonably unbiased estimates of the associated risk between acute bacterial gastroenteritis and long-term health sequelae.

Total and cause specific mortality among participants and non-participants of population based health surveys: a comprehensive follow up of 54 372 Finnish men and women

STUDY OBJECTIVE

To assess total and cause specific mortality among participants and non-participants of large population based health surveys.

DESIGN

A prospective follow up study. Baseline surveys were conducted in 1972, 1977, 1982, 1987, and 1992. Study end points were overall, cardiovascular, cancer and violent mortality, and deaths related to smoking and alcohol. Study cohorts were followed up until the end of 2000 through computerised record linkage. All analyses were adjusted for age.

SETTING

Finland.

PARTICIPANTS

Participants and non-participants of five population based risk factor surveys. The samples included 54 372 men and women aged 25 to 64 years at baseline.

MAIN RESULTS

The average participation rate was 81.7% among men and 87% among women. At eight year follow up, the non-participating men had twice and non-participating women 2.5-fold higher overall mortality than the participating men and women. Non-participants had also significantly higher cause specific mortality, except cancer and smoking related mortality among women. Relative differences in mortality were largest in violent and alcohol related deaths. Non-participants had considerably higher overall mortality than smoking participants, and their mortality was threefold compared with non-smoking participants.

CONCLUSIONS

Observed differences in mortality show that health behaviour and health status substantially differ between non-participants and participants. Low participation rate may considerably bias the results of population based health surveys.

Participation behavior of bladder cancer survivors in a medical follow-up survey on quality of life in France

The objectives were to ascertain the sociodemographic background of bladder cancer survivors acting on their participation behavior to a medical follow-up survey. This population-based quality of life (QOL) survey was realized by mail with 201 survivors (M:F = 171:30, median age = 74 years, range 33-99) randomly selected from the 1731 patients diagnosed between 1990 and 1994 in two regions of France. Response rate was 47.3%. Female and younger survivors were more receptive to the survey than were males and older survivors. Furthermore, survivors who had experienced a cystectomy were more responsive than those who did not. Similarly, the length of time since a major treatment was significant, with a shorter interval associated with a better response. The missing item rate in the QOL questionnaire was 13.8%. Other variables were not significantly associated with acceptance of the survey. Missing items among the responders were found more often in the sub-scale of social/familial well-being (15.6%). The older and male subjects left more questions blank. The reason for this low response rate can be categorized to the following three points: (1) Physically and psychologically not motivated to answer, (2) sensitive and private content of the question, and (3) methodological problem. Clearer concepts of the research would have helped the participants understand the objectives and better relate to the survey. Subsequently, these three issues should be given more attention in organizing questionnaire survey for improved participation rates in future studies.

Comparison of cause-specific mortality between respondents and nonrespondents in a population-based prospective study: ten-year follow-up of JPHC Study Cohort I. Japan Public Health Center

To evaluate the magnitude and duration of the "healthy volunteer effect" (HVE) in a middle-aged general population in Japan, we followed 54,396 subjects (26,998 men, 27,398 women) of the JPHC Study Cohort I from 1990 through 1999, and compared cause-specific mortality between respondents (79%) and nonrespondents to a baseline questionnaire survey. Age and area-adjusted RRs of mortality were higher among nonrespondents for all causes (2.02, 95% CI = 1.83-2.24), all cancers (1.43, 1.20-1.71), all circulatory system diseases (2.26, 1.86-2.74), and cerebrovascular disease (2.73, 2.04-3.66) in men, and 1.63 (1.39-1.92), 1.22 (0.94-1.58), 1.53 (1.07-2.20), and 1.65 (1.02-2.65), respectively, in women. These effects were not observed for ischemic heart disease. RR elevation for cancer was observed only in the first 2 years of follow-up (4.14, 2.74-6.26 versus 1.14, 0.93-1.40 after 2 years), while that for cerebrovascular disease was relatively stable for the entire period. In conclusion, HVE differed according to the causes and length of follow-up.

Comparison of the results between two diagnostic criteria by ADA and WHO among subjects with FPG 5.6-7.8 mmol/l in Kin-Hu and Kin-Chen, Kinmen, 1991-94

The objective of this study was to compare the results between two diagnostic criteria by ADA (1997) and WHO (1985) among those with fasting plasma glucose (FPG) level 5.6-7.8 mmol/l from a community-based survey in Kin-Hu and Kin-Chen, Kinmen conducted in 1991-94. According to official household registry, 10,797 residents aged over 30 were eligible for screening. 7580 had completed FPG screening and 1855 with FPG 5.6-7.8 mmol/l were invited to receive a 75-g oral glucose tolerance test (OGTT). 78.5% (1456/1855) had completed OGTT. The prevalence of impaired fasting glucose (IFG, by ADA) was 15.7%; the prevalence of impaired glucose tolerance (IGT, by WHO) was 22.7%; the prevalence of undiagnosed diabetes was 7.4% by ADA criteria and 10.9% by WHO criteria. It should be noticed that, among subjects with FPG 5.6-7.8 mmol/l, 50.3% of individuals with undiagnosed diabetes and 67.6% of individuals with IGT by WHO criteria would be missed by ADA criteria. Based on the above findings, the two-step screening strategy using FPG as the first line screening and OGTT for high-risk group (FPG 5.6-7.8 mmol/l) only was recommended in epidemiological study and case finding in consideration of feasibility and validity.

Protease inhibitor use among a community sample of people with HIV disease

OBJECTIVES

Protease inhibitors have become integral to HIV disease management. This paper examines sociodemographic factors affecting patient use and perceived knowledge of protease inhibitors, and the relationship between protease inhibitor use and perceived health.

METHODS

1034 people with HIV disease from a large AIDS services organization completed a mailed self-administered survey that assessed sociodemographics, protease inhibitor use and perceived knowledge, and perceived change in health status over the previous year. Multiple logistic regression was used to determine sociodemographic factors independently associated with protease inhibitor use and perceived knowledge, and perceived overall health status.

RESULTS

Two thirds (66%) of correspondents included in the sample were currently taking protease inhibitors and 52% reported being very knowledgeable about these medications. Adjusting for sociodemographic factors, those who were currently not taking protease inhibitors were more likely to be African American, non-English speaking, earning <$9600 U.S. annually, or uninsured. Among protease inhibitor users, those who reported less knowledge about the drugs were more likely to be nonwhite, earning <$9600 U.S. annually, and not college educated. Protease inhibitor use was independently associated with perceived improved overall health and having been college educated.

CONCLUSIONS

Further efforts should be directed toward increasing use and knowledge of protease inhibitors among disadvantaged populations.