The importance of post-hoc approaches for overcoming non-response and attrition bias in population-sampled studies

Population-based health studies are critical resources for monitoring population health and related factors such as substance use, but reliable inference can be compromised in various ways. Non-response and attrition are major methodological problems which reduce power and can hamper the generalizability of findings if individuals who participate and who remain in a study differ systematically from those who do not. In this issue of SPPE, McCabe et al. studied participants of the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions, comparing attrition in Wave 2 across participants with different patterns of substance use at Wave 1. The implications of differential follow-up and further possibilities for addressing selective participation are discussed

What is wrong with non-respondents? Alcohol-, drug- and smoking related mortality and morbidity in a 12-year follow up study of respondents and non-respondents in the Danish Health and Morbidity Survey

Aim: Response rates in health surveys have diminished over the last two decades, making it difficult to obtain reliable information on health and health-related risk factors in different population groups. This study compared cause-specific mortality and morbidity among survey respondents and different types of non-respondents to estimate alcohol-, drug- and smoking related mortality and morbidity among non-respondents. Design: Prospective follow-up study of respondents and non-respondents in two cross-sectional health surveys. Setting: Denmark. Participants: A total sample of 39,540 Danish citizens aged 16 or older. Measurements: Register-based information on cause-specific mortality and morbidity at the individual level was obtained for respondents (n=28,072) and different types of non-respondents (refusals n=8,954; illness/disabled n=731, uncontactable n=1,593). Cox proportional hazards models were used to examine differences in alcohol-, drug- and smoking-related mortality and morbidity, respectively, in a 12 year follow-up period. Findings: Overall, non-response was associated with a significantly increased hazard ratio of 1.56 (95% CI: 1.36–1.78) for alcohol-related morbidity, 1.88 (95% CI: 1.38-2.57) for alcohol-related mortality, 1.55 (95% CI: 1.27–1.88) for drug-related morbidity, 3.04 (95% CI: 1.57–5.89) for drug-related mortality and 1.15 (95% CI: 1.03–1.29) for smoking-related morbidity. The hazard ratio for smoking-related mortality also tended to be higher among non-respondents compared with respondents although no significant association was evident (HR: 1.14; 95% CI: 0.95-1.36). Uncontactable and ill/disabled non-respondents generally had a higher hazard ratio of alcohol-, drug- and smoking related mortality and morbidity compared with refusal non-respondents. Conclusion: Health survey non-respondents in Denmark have an increased hazard ratio of alcohol-, drug-, and smoking-related mortality and morbidity compared with respondents, which may indicate more unfavourable health behaviours among non-respondents

Socioeconomic status as an effect modifier of alcohol consumption and harm: an analysis of linked cohort data

Background: Alcohol-related mortality and morbidity are higher in socioeconomically disadvantaged populations. It is unclear if elevated harm reflects differences in consumption, reverse causation or greater risk of harm following similar consumption. We investigated whether the harmful effects differed by socioeconomic status accounting for alcohol consumption and other health-related factors. Methods: Alcohol consumption (weekly units and binge drinking) data (n=50,236; 429,986 person-years of follow-up) were linked to deaths, hospitalisations and prescriptions. The primary outcome was alcohol-attributable hospitalisation/death. The relationship between alcohol attributable harm and socioeconomic status was investigated for four measures (education level, social class, household income and area-based deprivation) using Cox proportional hazards models. The potential for alcohol consumption and other risk factors mediating the social patterning was explored. Downward social selection for high-risk drinkers (reverse causation) was tested by comparing change in area deprivation over time. Findings: Low socioeconomic status was consistently associated with markedly elevated alcohol-attributable harms, including after adjustment for weekly consumption, binge drinking, body mass index and smoking. There was evidence of effect modification: for example, relative to light drinkers living in advantaged areas, the hazard ratio for excessive drinkers was 6.75 (95% CI 5.09-8.93) in advantaged and 11.06 (95% CI 8.53-14.35) in deprived areas. We found little support for downward social selection. Interpretation: Disadvantaged social groups experience greater alcohol-attributable harms compared to the advantaged for given levels of alcohol consumption, even after accounting for different drinking patterns, obesity and smoking status at the individual level

Youth vaping and smoking and parental vaping: a panel survey

Background: Concerns remain about potential negative impacts of e-cigarettes including possibilities that: youth e-cigarette use (vaping) increases risk of youth smoking; and vaping by parents may have impacts on their children’s vaping and smoking behaviour. Methods: With panel data from 3291 youth aged 10–15 years from the 7th wave of the UK Understanding Society Survey (2015–2017), we estimated effects of youth vaping on youth smoking (ever, current and past year initiation), and of parental vaping on youth smoking and vaping, and examined whether the latter differed by parental smoking status. Propensity weighting was used to adjust for measured confounders and estimate average effects of vaping for all youth, and among youth who vaped. E-values were calculated to assess the strength of unmeasured confounding influences needed to negate our estimates. Results: Associations between youth vaping and youth smoking were attenuated considerably by adjustment for measured confounders. Estimated average effects of youth vaping on youth smoking were stronger for all youth (e.g. OR for smoking initiation: 32.5; 95% CI: 9.8–107.1) than among youth who vaped (OR: 4.4; 0.6–30.9). Relatively strong unmeasured confounding would be needed to explain these effects. Associations between parental vaping and youth vaping were explained by measured confounders. Estimates indicated effects of parental vaping on youth smoking, especially for youth with ex-smoking parents (e.g. OR for smoking initiation: 11.3; 2.7–46.4) rather than youth with currently smoking parents (OR: 1.0; 0.2–6.4), but these could be explained by relatively weak unmeasured confounding. Conclusions While measured confounding accounted for much of the associations between youth vaping and youth smoking, indicating support for underlying propensities, our estimates suggested residual effects that could only be explained away by considerable unmeasured confounding or by smoking leading to vaping. Estimated effects of youth vaping on youth smoking were stronger among the general youth population than among the small group of youth who actually vaped. Associations of parental vaping with youth smoking and vaping were either explained by measured confounding or could be relatively easily explained by unmeasured confounding

Explaining the social patterning of lung function in adulthood at different ages: the roles of childhood precursors, health behaviours and environmental factors

Background: Lung function successfully predicts subsequent health. Although lung function is known to decline over age, little is known about changes in association with socioeconomic status (SES) throughout life, and whether explanatory factors for association vary with age or patterns for non smokers. Methods: Analyses were based on data on 24 500 participants aged ≥ 18 years from the 1995, 1998 and 2003 Scottish Health Surveys who were invited to provide 1 s forced expiratory volume (FEV1) and forced vital capacity (FVC) lung measurements. Sex-stratified multiple linear regression assessed lung function-SES (occupational social class) associations and attenuation by covariates in three age groups (2003 data (n=7928)). Results: The FEV1-SES patterns were clear ( p<0.001) and constant over time. Relative to the least disadvantaged, FEV1 in the most disadvantaged was lower by 0.28 L in men and 0.20 L in women under 40 years compared with differences of 0.51 L in men and 0.25 L in women over 64 years (pinteraction<0.001 men, pinteraction=0.004 women). The greatest attenuation of these results was seen by height, parental social class and smoking, especially among the under 65s. Secondhand smoke exposure and urban/rural residence had some impact among older groups. Adjusting for physical activity and weight had little effect generally. Similar patterns were seen for FVC and among never smokers. Conclusions: We found cross-sectional evidence that SES disparity in lung function increases with age, especially for men. Our findings indicate that early-life factors may predict inequity during younger adulthood, with environmental factors becoming more important at older ages

Assessing progress in protecting non-smokers from secondhand smoke

Objective To examine trends in population exposure to second-hand tobacco smoke (SHS) and consider two exposure metrics as appropriate targets for tobacco control policymakers. Design Comparison of adult non-smokers’ salivary cotinine data available from eleven Scottish Health Surveys between 1998 and 2016. Methods The proportions of non-smoking adults who had measurable levels of cotinine in their saliva were calculated for the eleven time points. The Geometric Mean (GM) concentrations of cotinine levels were calculated using Tobit regression. Changes in both parameters were assessed for the whole period and also for the years since implementation of smoke-free legislation in Scotland in 2006. Results Salivary cotinine expressed as a GM fell from 0.464 ng/ml (95% CI 0.444-0.486 ng/ml) in 1998 to 0.013 ng/ml (95% CI 0.009-0.020 ng/ml) in 2016: a reduction of 97.2%. The percentage of non-smoking adults who had no measurable cotinine in their saliva increased by nearly six-fold between 1998 (12.5% [95% CI 11.5%-13.6%]) and 2016 (81.6% [95% CI 78.6%-84.6%]). Reductions in population exposure to SHS have continued even after smoke-free legislation in 2006. Conclusions Scotland has witnessed a dramatic reduction in SHS exposure in the past two decades but there are still nearly one in five non-smoking adults who have measurable exposure to SHS on any given day. Tobacco control strategies globally should consider the use of both the proportion of non-smoking adults with undetectable salivary cotinine and the GM as targets to encourage policies that achieve a smoke-free future

How healthy are survey respondents compared with the general population? Using survey-linked death records to compare mortality outcomes

Background: National surveys are used to capture US health trends and set clinical guidelines, yet the sampling frame often includes those in non-institutional households, potentially missing those most vulnerable for poor health. Declining response rates in national surveys also represent a challenge, and existing inputs to survey weights have limitations. We compared mortality rates between those who respond to surveys and the general population over time. Methods: Survey respondents from twenty waves of the National Health Interview Survey from 1990 through 2009 who have been linked to death records through 31 December 2011 were included. For each cohort in the survey, we estimated their mortality rates along with that cohort's mortality rate in the census population using vital statistics records and differences were examined using Poisson models. Results: In all years, survey respondents had lower mortality rates compared with the general population, when data were both weighted and unweighted. Among men, survey respondents in the weighted sample had 0.86 (95% C.I. 0.853-0.868) times the mortality rate of the general population (among women, RR=0.887; 95% C.I. 0.879-0.895). Differences in mortality are evident along all points of the life course. Differences have remained relatively stable over time. Conclusion: Survey respondents have lower death rates than the general US population, suggesting that they are a systematically healthier source population. Incorporating non-household samples and revised weighting strategies to account for sample frame exclusion and non-response may allow for more rigorous estimation of the US population's health

Trends in adult cardiovascular disease risk factors and their socio-economic patterning in the Scottish population 1995–2008: cross-sectional surveys

&lt;p&gt;Objectives To examine secular and socio-economic changes in cardiovascular disease risk factor prevalences in the Scottish population. This could contribute to a better understanding of why the decline in coronary heart disease mortality in Scotland has recently stalled along with a widening of socio-economic inequalities.&lt;/p&gt; &lt;p&gt;Design Four Scottish Health Surveys 1995, 1998, 2003 and 2008 (6190, 6656, 5497 and 4202 respondents, respectively, aged 25–64 years) were used to examine gender-stratified, age-standardised prevalences of smoking, alcohol consumption, physical activity, fruit and vegetable consumption, discretionary salt use and self-reported diabetes or hypertension. Prevalences were determined according to education and social class. Inequalities were assessed using the slope index of inequality, and time trends were determined using linear regression.&lt;/p&gt; &lt;p&gt;Results There were moderate secular declines in the prevalence of smoking, excess alcohol consumption and physical inactivity. Smoking prevalence declined between 1995 and 2008 from 33.4% (95% CI 31.8% to 35.0%) to 29.9% (27.9% to 31.8%) for men and from 36.1% (34.5% to 37.8%) to 27.4% (25.5% to 29.3%) for women. Adverse trends in prevalence were noted for self-reported diabetes and hypertension. Over the four surveys, the diabetes prevalence increased from 1.9% (1.4% to 2.4%) to 3.6% (2.8% to 4.4%) for men and from 1.7% (1.2% to 2.1%) to 3.0% (2.3% to 3.7%) for women. Socio-economic inequalities were evident for almost all risk factors, irrespective of the measure used. These social gradients appeared to be maintained over the four surveys. An exception was self-reported diabetes where, although inequalities were small, the gradient increased over time. Alcohol consumption was unique in consistently showing an inverse gradient, especially for women.&lt;/p&gt; &lt;p&gt;Conclusions There has been only a moderate decline in behavioural cardiovascular risk factor prevalences since 1995, with increases in self-reported diabetes and hypertension. Adverse socio-economic gradients have remained unchanged. These findings could help explain the recent stagnation in coronary heart disease mortalities and persistence of related inequalities.&lt;/p&gt

Trends in cardiovascular disease biomarkers and their socioeconomic patterning among adults in the Scottish population 1995 to 2009: cross-sectional surveys

Objectives To examine secular and socioeconomic changes in biological cardiovascular disease risk factor and biomarker prevalences in the Scottish population. This could contribute to an understanding of why the decline in coronary heart disease mortality in Scotland has recently stalled along with persistence of associated socioeconomic inequalities. Design Cross-sectional surveys. Setting Scotland. Participants Scottish Health Surveys: 1995, 1998, 2003, 2008 and 2009 (6190, 6656, 5497, 4202 and 4964 respondents, respectively, aged 25–64 years). Primary outcome measures Gender-stratified, age-standardised prevalences of obesity, hypertension, hypercholesterolaemia and low high-density lipoprotein cholesterol blood concentration as well as elevated fibrinogen and C reactive protein concentrations according to education and social class groupings. Inequalities were assessed using the slope index of inequality, and time trends were assessed using linear regression. Results The prevalence of obesity, including central obesity, increased between 1995 and 2009 among men and women, irrespective of socioeconomic position. In 2009, the prevalence of obesity (defined by body mass index) was 29.8% (95% CI 27.9% to 31.7%) for men and 28.2% (26.3% to 30.2%) for women. The proportion of individuals with hypertension remained relatively unchanged between 1995 and 2008/2009, while the prevalence of hypercholesterolaemia declined in men from 79.6% (78.1% to 81.1%) to 63.8% (59.9% to 67.8%) and in women from 74.1% (72.6% to 75.7%) to 66.3% (62.6% to 70.0%). Socioeconomic inequalities persisted over time among men and women for most of the biomarkers and were particularly striking for the anthropometric measures when stratified by education. Conclusions If there are to be further declines in coronary heart disease mortality and reduction in associated inequalities, then there needs to be a favourable step change in the prevalence of cardiovascular disease risk factors. This may require radical population-wide interventions

Standard multiple imputation of survey data didn’t perform better than simple substitution in enhancing an administrative dataset: the example of self-rated health in England

Background: Health surveys provide a rich array of information but on relatively small numbers of individuals and evidence suggests that they are becoming less representative as response levels fall. Routinely collected administrative data offer more extensive population coverage but typically comprise fewer health topics. We explore whether data combination and multiple imputation of health variables from survey data is a simple and robust way of generating these variables in the general population. Methods: We use the UK Integrated Household Survey and the English 2011 population census both of which included self-rated general health. Setting aside the census self-rated health data we multiply imputed self-rated health responses for the census using the survey data and compared these with the actual census results in 576 unique groups defined by age, sex, housing tenure and geographic region. Results: Compared with original census data across the groups, multiply imputed proportions of bad or very bad self-rated health were not a markedly better fit than those simply derived from the survey proportions. Conclusion: While multiple imputation may have the potential to augment population data with information from surveys, further testing and refinement is required