A novel framework for classification of selection processes in epidemiological research

BACKGROUND

Selection and selection bias are terms that lack consistent definitions and have varying meaning and usage across disciplines. There is also confusion in current definitions between underlying mechanisms that lead to selection and their consequences. Consequences of selection on study validity must be judged on a case-by-case basis depending on research question, study design and analytical decisions. The overall aim of the study was to develop a simple but general framework for classifying various types of selection processes of relevance for epidemiological research.

METHODS

Several original articles from the epidemiological literature and from related areas of observational research were reviewed in search of examples of selection processes, used terminology and description of the underlying mechanisms.

RESULTS

We classified the identified selection processes in three dimensions: i) selection level (selection at the population level vs. study-specific selection), ii) type of mechanism (selection in exposure vs. selection in population composition), iii) timing of the selection (at exposure entry, during exposure/follow-up or post-outcome).

CONCLUSIONS

Increased understanding of when, how, and why selection occur is an important step towards improved validity of epidemiological research.

Assessment of selection bias due to dropouts in the follow-up of the Scania Public Health Cohort

Aims: To investigate potential differences between participants and dropouts in the 2005 follow-up of the Scania Public Health Cohort Study regarding the prevalence of commonly studied health determinants and whether these factors had differential associations with three health outcomes: all-cause mortality and purchase of prescribed cardiovascular or psychotropic drugs during a 10-year follow-up period. Methods: The Scania Public Health Cohort was initiated in 1999/2000, with randomly invited participants aged 18–80 years from the general population (58% participation). Questionnaire data from 10,462 participants and 2576 dropouts in the 2005 follow-up (80% participation) were linked to public registers on mortality and purchase of prescribed drugs. Results: Age, male gender, being born abroad, low educational level, low self-rated mental and general health and daily smoking were all related to dropping out. The 10-year mortality was higher among dropouts (13.4% versus 11.9%; age-adjusted hazard ratio 1.6, 95% confidence interval: 1.4–1.8). In 13 out of 18 analyses, similar associations between health determinants and outcomes were found across participants and dropouts. However, being born outside of Sweden was associated with higher risks for all three poor health outcomes among participants, but not so among dropouts. Conclusions: Despite selective participation at follow-up, there was little evidence of selection bias, insofar as estimated associations were generally similar across participants, dropouts and the whole cohort. This finding is important for the assessment of the validity of prospective findings from this cohort and similar ones, where the loss of individuals at consecutive follow-ups of exposure is non-negligible.

Longitudinal association between housing accessibility and activities of daily living: the role of self-efficacy and control in people ageing with Parkinson's disease

Background

External housing-related control beliefs (HCB) and general self-efficacy (GSE) influence different health outcomes in the general ageing population, but there is no information of their role in people ageing with Parkinson’s disease (PD). This study aimed to longitudinally assess the role of external HCB and GSE on the association between housing accessibility and activities of daily living (ADL) among people ageing with PD.

Methods

Baseline and 3-year follow-up data on 130 community-living participants from the Swedish project ‘Home and Health in People Ageing with PD’ were collected. Assessments addressed housing accessibility, external HCB, GSE, generic ADL and ADL specific to PD. The moderating effects of external HCB and GSE were assessed by including an interaction term in multivariable logistic regression.

Results

There were statistically significant interactions between housing accessibility and GSE on ADL (p = 0.03), and housing accessibility and external HCB on PD specific ADL (p = 0.03). After stratifying the analyses by GSE, housing accessibility problems led to more dependence and difficulty in ADL in participants with low GSE (OR 1.14; 95% CI 1.02–1.28). After stratifying by external HCB, housing accessibility increased dependence and difficulty in PD specific ADL in participants with low external HCB (OR 1.35; 95% CI 1.03–1.76).

Discussion

The results suggest that housing accessibility predicts ADL in people with PD with GSE and external HCB playing a moderating role for generic ADL and ADL specific to PD, respectively. Further longitudinal studies should validate these findings and explore their potential application in PD-related care and rehabilitation.

Hand strength and dexterity in individuals with hand eczema

BACKGROUND

Patients with hand eczema often describe symptoms such as pain, clumsiness and difficulty flexing their fingers, thus impairing the function of the hand.

OBJECTIVE

The aim of this study was to investigate whether hand eczema is associated with a measurable impairment of hand strength and dexterity. We also studied the relationship between hand function and the ability to perform activities of daily living (ADL), pain level and quality of life measured with the Dermatology Life Quality Index (DLQI).

METHODS

Twenty-one participants with ongoing hand eczema were examined with well-established methods for measuring hand grip strength, pinch strength and dexterity. A questionnaire was designed to investigate perceived ability to perform ADL. The participants were also asked to grade their current pain level, and the DLQI was used to assess the participants' quality of life. A group of 12 participants was reinvestigated when healed.

RESULTS

The participants demonstrated a significant improvement in all functional tests when healed. There was a strong correlation between ADL and both dexterity and hand grip strength. There was also a strong correlation between ADL and pain. All participants reported some difficulty performing ADL.

CONCLUSIONS

Our results suggest that ongoing hand eczema may lead to a measurable decrease of strength and dexterity of the hand, leading to an impairment of the ability to perform ADL and consequently to a poorer quality of life.

Early-life social and health determinants of adult socioeconomic position: associations and trends across generations

Background

Social and biological circumstances at birth are established predictors of adult socioeconomic position (SEP). This study aims to assess the trends in these associations across two generations and examine the effects of parental early-life characteristics on descendants’ adult SEP.

Methods

We studied men and women born in the Uppsala University Hospital 1915–1929 (G1) and their offspring born 1932–1960 (G2). Data were collected in archives and routine registers. Adult SEP was assessed as an aggregate measure combining education and occupation. The exposures were family SEP, mother’s marital status, mother’s parity, mother’s age, standardised birth weight, gestational length and birth multiplicity. Linear regression was used to examine the associations across generations.

Results

The difference in adult SEP between low and high family SEP at birth was 15.8 (95% CI: 13.3 to 18.3) percentage points smaller in G2 compared with G1, although a considerable difference was still evident in G2. The associations of adult SEP with small birth weight for gestational age, post-term birth and high parity were stable between the generations: the generational differences in adjusted coefficients were 1.5 (95% CI: −1.1 to 4.1), 0.6 (–1.7 to 2.9) and 1.8 (–0.2 to 3.8) percentage points, respectively. The association between grandparental and grandchildren’s SEPs was largely explained by parental socioeconomic conditions. Father’s preterm birth was independently associated with offspring’s SEP.

Conclusion

The stability of the associations between early-life biological disadvantages and adult SEP and the persistent, although attenuated, association between early-life and adult SEPs necessitates increased policy attention to both social and health conditions at birth.

Proposed Classification of Incision Complications: Analysis of a Prospective Study on Elective Open Lower-Limb Revascularization

Background: Incision complications (IC) have a significant impact on procedure-related morbidity after lower-limb revascularization. One of the most studied IC is surgical site infection (SSI). Reporting these complications in a uniform way is crucial to evaluate treatment approaches. The aim of this study was to propose a comprehensive classification of IC and apply it to compare SSI with other IC in a trial on elective open lower-limb revascularization procedures. Methods: Two hundred twenty-three eligible patients undergoing elective unilateral inguinal and infra-inguinal arterial vascular surgery were extracted from a randomized controlled trial on incisional negative-pressure wound therapy (NPWT) on inguinal vascular surgical incisions. The IC were classified by grades of severity (grade 0-6) that focused on IC-related consequences such as out-patient treatment (grade 1), prolonged in-patient treatment (grade 2), re-admission (grade 3), and re-operation (grade ≥4). An SSI was defined by the ASEPSIS score criteria. Results: An SSI was diagnosed in 63 patients (28.3%). Thirty-five of 160 patients (21.8%) not suffering from SSI underwent IC treatment. Treatment for IC was recorded for 25/144 patients (17.4%) with satisfactory site healing as judged by the ASEPSIS score. The median incision-related in-hospital stay in those with SSI (n = 79) and disturbed healing (n = 16) according to the ASEPSIS score was 13 days in both groups (p = 0.53). Five patients had peri-vascular SSI (IC grade 4 n = 4; grade 5 n = 1). The proposed classification of IC and the ASEPSIS score correlated highly (r = 0.77; p < 0.001). Inter-rater reliability for IC grading was substantial for three investigators with different levels of experience (k = 0.81, 0.71, and 0.70). Conclusions: The proposed incision classification suggests a comparable clinical significance of vascular IC in terms of IC-related in-patient stay, whether there was a surgical site infection or not. This classification system requires external validation.

Correcting for selective participation in cohort studies using auxiliary register data without identification of non-participants

Aims: Selective participation may hamper the validity of population-based cohort studies. The resulting bias can be alleviated by linking auxiliary register data to both the participants and the non-participants of the study, estimating propensity scores for participation and correcting for participation based on these. However, registry holders may not be allowed to disclose sensitive data on (invited) non-participants. Our aim is to provide guidance on how adequate bias correction can be achieved by using auxiliary register data but without disclosing information that could be linked to the subset of non-participants. Methods: We show how existing methods can be used to estimate generalisation weights under various data disclosure scenarios where invited non-participants are indistinguishable from uninvited ones. We also demonstrate how the methods can be implemented using Nordic register data. Results: Inverse-probability-of-sampling weights estimated within a random sample of the target population in which the non-respondents are disclosed are equivalent in expectation to analogous weights in a scenario where the non-participants and uninvited individuals from the population are indistinguishable. To minimise the risk of disclosure when the entire population is invited to participate, investigators should instead consider inverse-odds-of-sampling weights, a method that has previously been suggested for transporting study results to external populations. Conclusions: Generalisation weights can be estimated from auxiliary register data without disclosing information on invited non-participants.

Commonly used estimates of the genetic contribution to disease are subject to the same fallacies as bad luck estimates

The scientific debate following the initial formulation of the "bad luck" hypothesis in cancer development highlighted how measures based on analysis of variance are inappropriately used for risk communication. The notion of "explained" variance is not only used to quantify randomness, but also to quantify genetic and environmental contribution to disease in heritability coefficients. In this paper, we demonstrate why such quantifications are generally as problematic as bad luck estimates. We stress the differences in calculation and interpretation between the heritability coefficient and the population attributable fraction, the estimated fraction of all disease events that would not occur if an intervention could successfully prevent the excess genetic risk. We recommend using the population attributable fraction when communicating results regarding the genetic contribution to disease, as this measure is both more relevant from a public health perspective and easier to understand.

Quantum Tunneling Mediated Interfacial Synthesis of a Benzofuran Derivative

Reaction pathways involving quantum tunneling of protons are fundamental to chemistry and biology. They are responsible for essential aspects of interstellar synthesis, the degradation and isomerization of compounds, enzymatic activity, and protein dynamics. On-surface conditions have been demonstrated to open alternative routes for organic synthesis, often with intricate transformations not accessible in solution. Here, we investigate a hydroalkoxylation reaction of a molecular species adsorbed on a Ag(111) surface by scanning tunneling microscopy complemented by X-ray electron spectroscopy and density functional theory. The closure of the furan ring proceeds at low temperature (down to 150 K) and without detectable side reactions. We unravel a proton-tunneling-mediated pathway theoretically and confirm experimentally its dominant contribution through the kinetic isotope effect with the deuterated derivative.

Nationwide study of appendicitis in children

Background

Paediatric surgical care is increasingly being centralized away from low‐volume centres, and prehospital delay is considered a risk factor for more complicated appendicitis. The aim of this study was to determine the incidence of paediatric appendicitis in Sweden, and to assess whether distance to the hospital was a risk factor for complicated disease.

Methods

A nationwide cohort study of all paediatric appendicitis cases in Sweden, 2001–2014, was undertaken, including incidence of disease in different population strata, with trends over time. The risk of complicated disease was determined by regression methods, with travel time as the primary exposure and individual‐level socioeconomic determinants as independent variables.

Results

Some 38 939 children with appendicitis were identified. Of these, 16·8 per cent had complicated disease, and the estimated risk of paediatric appendicitis by age 18 years was 2·5 per cent. Travel time to the treating hospital was not associated with complicated disease (adjusted odds ratio (OR) 1·00 (95 per cent c.i. 0·96 to 1·05) per 30‐min increase; P = 0·934). Level of education (P = 0·177) and family income (P = 0·120) were not independently associated with increased risk of complicated disease. Parental unemployment (adjusted OR 1·17, 95 per cent c.i. 1·05 to 1·32; P = 0·006) and having parents born outside Sweden (1 parent born in Sweden: adjusted OR 1·12, 1·01 to 1·25; both parents born outside Sweden: adjusted OR 1·32, 1·18 to 1·47; P < 0·001) were associated with an increased risk of complicated appendicitis.

Conclusion

Every sixth child diagnosed with appendicitis in Sweden has a more complicated course of disease. Geographical distance to the surgical facility was not a risk factor for complicated appendicitis.

Burnout among school teachers: quantitative and qualitative results from a follow-up study in southern Sweden

Background

Teachers are at high risk of stress-related disorders. This longitudinal study aimed to (a) identify which occupational, sociodemographic and life-style factors and self-efficacy at baseline that were of importance for burnout, (b) explore associations between changes in the studied factors versus changes in burnout, and (c) by interviews increase the understanding of perceived job demands among teachers.

Methods

A cohort of 310 Swedish teachers in school-years 4–9 responded to a questionnaire of occupational, sociodemographic and life-style factors, self-efficacy and burnout, at baseline and at follow-up (mean 30 months later). A combined measure with four levels of burnout was crafted, based on exhaustion, cynicism and professional efficacy (Maslach Burnout Inventory-General Survey). Quantitative data were analysed with multiple ordinal regression, and qualitative data were analysed with content analysis of interview responses from a subgroup of the teachers (n = 81).

Results

The occurrence of high burnout (level 2 and 3 combined) were similar at baseline and follow-up (14% vs. 15%). However, many teachers fluctuated between the levels of burnout (28% increased and 24% decreased). Burnout at baseline was of importance for change of work or being off duty at follow up. In the multi-exposure model, low self-efficacy [OR 0.42; CI 0.26–0.68] and high job demands [OR 1.97; CI 1.02–3.8] were the strongest explanatory variables. Low self-efficacy remained as the strongest explanatory factor after adjustment for burnout at baseline. Increased job demands during follow-up was associated with an increased level of burnout [OR 3.41; CI 1.73–6.69], whereas increased decision latitude was associated with a decreased level of burnout [OR 0.51; CI 0.30–0.87]. Two major categories of demands emerged in the qualitative analysis; i.e. too high workload and a sense of inadequacy.

Conclusions

A substantial proportion of teachers showed signs of burnout at both occasions. Low self-efficacy and high job demands was of importance for burnout, and changes in burnout was further associated with changes in decision latitude. The results points to the need of actions on individual, organizational and a societal levels.

Electronic supplementary material

The online version of this article (10.1186/s12889-019-6972-1) contains supplementary material, which is available to authorized users.

Prognostic performance of preoperative cardiac troponin and perioperative changes in cardiac troponin for the prediction of major adverse cardiac events and mortality in noncardiac surgery: A systematic review and meta-analysis

Background

Increased postoperative cardiac troponin (cTn) independently predicts short-term mortality. Previous studies suggest that preoperative cTn also predicts major adverse cardiovascular events (MACE) and mortality after noncardiac surgery. The value of preoperative and perioperative changes in cTn as a prognostic tool for adverse outcomes has been sparsely investigated.

Methods and findings

A systematic review and meta-analysis of the prognostic value of cTns for adverse outcome was conducted. Adverse outcome was defined as short-term (in-hospital or <30 days) and long-term (>30 days) MACE and/or all-cause mortality, in adult patients undergoing noncardiac surgery. The study protocol (CRD42018094773) was registered with an international prospective register of systematic reviews (PROSPERO). Preoperative cTn was a predictor of short- (OR 4.3, 95% CI 2.9–6.5, p<0.001, adjusted OR 5.87, 95% CI 3.24–10.65, p<0.001) and long-term adverse outcome (OR 4.2, 95% CI 1.0–17.3, p = 0.05, adjusted HR 2.0, 95% CI 1.4–3.0, p<0.001). Perioperative change in cTn was a predictor of short-term adverse outcome (OR 10.1, 95% CI 3.2–32.3, p<0.001). It was not possible to conduct pooled analyses for adjusted estimates of perioperative change in cTn as predictor of short- (a single study identified) and long-term (no studies identified) adverse outcome. Further, it was not possible to conduct pooled analyses for unadjusted estimates of perioperative change in cTn as predictor of long-term adverse outcome, since only one study was identified. Bivariate analysis of sensitivities and specificities were performed, and overall prognostic performance was summarized using summary receiver operating characteristic (SROC) curves. The pooled sensitivity and specificity for preoperative cTn and short-term adverse outcome was 0.43 and 0.86 respectively (area under the SROC curve of 0.68). There were insufficient studies to construct SROCs for perioperative changes in cTn and for long-term adverse outcome.

Conclusion

Our study indicates that although preoperative cTn and perioperative change in cTn might be valuable predictors of MACE and/or all-cause mortality in adult noncardiac surgical patients, its overall prognostic performance remains uncertain. Future large, representative, high-quality studies are needed to establish the potential role of cTns in perioperative cardiac risk stratification.

Work-related neck and upper limb disorders - quantitative exposure-response relationships adjusted for personal characteristics and psychosocial conditions

BACKGROUND

We have previously reported quantitative exposure-response relationships between physical exposures recorded by technical methods, and complaints and diagnoses in the neck/shoulders, and the elbows/hands, based on group data. In the present study the number of workers was doubled, and information on individual factors, and psychosocial working conditions was used. Relationships between various kinds of exposure and response have been analysed in this larger and more detailed sample.

METHODS

The prevalence of complaints (Nordic Questionnaire) and diagnoses (clinical examination) were recorded in a number of occupational groups within which the participants had similar work tasks, 34 groups of female employees (N = 4733 women) and 17 groups of male employees (N = 1107 men). Age and other individual characteristics were recorded, as well as psychosocial work environment factors (job-content questionnaire) for most participants. Postures and velocities (inclinometry) of the head (N = 505) and right upper arm (N = 510), right wrist postures and velocities (electrogoniometry; N = 685), and muscular activity (electromyography; EMG) in the right trapezius muscle (N = 647) and forearm extensors (N = 396) were recorded in representative sub-groups. Exposure-response relationships between physical exposure and musculoskeletal disorders, adjusted for individual factors with Poisson regression were then calculated. The effect of introducing psychosocial conditions into the models was also assessed.

RESULTS

Associations were found between head velocity, trapezius activity, upper arm velocity, forearm extensor activity and wrist posture and velocity, and most neck/shoulder and elbow/hand complaints and diagnoses. Adjustment for age, other individual characteristics and psychosocial work conditions had only a limited effect on these associations. For example, the attributable fraction for tension neck syndrome among female workers with the highest quintile of trapezius activity was 58%, for carpal tunnel syndrome versus wrist velocity it was 92% in men in the highest exposure quintile.

CONCLUSIONS

Based on the findings, we propose threshold limit values for upper arm and wrist velocity.

Skin exposure to the rubber accelerator diphenylguanidine in medical gloves-An experimental study

BACKGROUND

Dermatitis caused by occupational contact allergy to rubber additives such as diphenylguanidine (DPG) in medical gloves is a hazard for healthcare workers. Both the duration of exposure to medical gloves and the number of gloves used per day vary. The use of alcoholic skin disinfectants before glove donning is mandatory.

OBJECTIVES

To assess whether skin exposure to the rubber accelerator DPG released from glove material is influenced by alcoholic hand disinfectants, time, and pH.

METHODS

With the use of ethanol washes, the amount of DPG left on the hands after wearing of gloves for 60 minutes was measured, and comparisons between hands exposed and not exposed to alcoholic disinfectant before glove donning were made. With the use of artificial sweat buffered at pH 4, 5, and 6, DPG release from the insides of gloves at different times was measured.

RESULTS

The use of alcoholic disinfectant prior to polyisoprene glove donning increased the amount of DPG recovered from the hands. Of the DPG released from polyisoprene gloves into artificial sweat, almost 84% was released within 10 minutes. pH did not influence the rate of release.

CONCLUSIONS

The use of alcoholic disinfectant increased skin exposure to the rubber accelerator DPG. Even a short duration of use of gloves results in substantial exposure to DPG.

Most gene fusions in cancer are stochastic events

Cancer-associated gene fusions resulting in chimeric proteins or aberrant expression of one or both partner genes are pathogenetically and clinically important in several hematologic malignancies and solid tumors. Since the advent of different types of massively parallel sequencing (MPS), the number of identified gene fusions has increased dramatically, prompting the question whether they all have a biologic impact. By ascertaining the chromosomal locations of 8934 genes involved in 10 861 gene fusions reported in the literature, we here show that there is a highly significant association between gene content of chromosomes and chromosome bands and number of genes involved in fusions. This strongly suggests that a clear majority of gene fusions detected by MPS are stochastic events associated with the number of genes available to participate in fusions and that most reported gene fusions are passengers without any pathogenetic importance.

Watching nanostructure growth: kinetically controlled diffusion and condensation of Xe in a surface metal organic network

Diffusion, nucleation and growth provide the fundamental access to control nanostructure growth. In this study, the temperature activated diffusion of Xe at and between different compartments of an on-surface metal organic coordination network on Cu(111) has been visualized in real space. Xe atoms adsorbed at lower energy sites become mobile with increased temperature and gradually populate energetically more favourable binding sites or remain in a delocalized 'fluid' form confined to diffusion along a topological subset of the on-surface network. These diffusion pathways can be studied individually under kinetic control via the chosen thermal energy kT of the sample and are determined by the network and sample architecture. The spatial distribution of Xe in its different modes of mobility and the time scales of the motion is revealed by Scanning Tunneling Microscopy (STM) at variable temperatures up to 40 K and subsequent cooling to 4 K. The system provides insight into the diffusion of a van der Waals gas on a complex structured surface and its nucleation and coarsening/growth into larger condensates at elevated temperature under thermodynamic conditions.

Predictors of chronic pain intensity, spread, and sensitivity in the general population: A two-year follow-up study from the SWEPAIN cohort

OBJECTIVE

To determine whether the intensity, spread and sensitivity of chronic pain can be predicted using demographic features, socioeconomic conditions and comorbidities.

DESIGN

A longitudinal study design was employed. Data was collected at baseline and at 2-year follow-up.

SETTING

General population in south-eastern Sweden.

SUBJECTS

A representative stratified random sample of 34,000 individuals, between 18 and 85 years of age, selected from a sampling frame of 404,661 individuals based on the Swedish Total Population Register.

METHODS

Eligible individuals were sent postal surveys in 2013 and 2015. The 2 surveys included the same questions about basic demographic data, comorbidities, and chronic pain intensity, spread and sensitivity.

RESULTS

Several socio-demographic features and comorbidities at baseline were significant predictors of characteristics of pain (intensity, spread and sensitivity) at the 2-year follow-up. When characteristics of pain at baseline were included in the regression analyses they were relatively strong significant predictors of characteristics of pain after 2 years. After this adjustment there were fewer socio-demogra-phic and comorbidity predictors; the effect estimates for those significant predictors had decreased.

CONCLUSION

Clinical assessment should focus on several characteristics of pain and include a broad medical screening to capture the overall burden of pain in adults from a longitudinal perspective.