Showing papers in "International Journal of Epidemiology in 2016"

Interrupted time series regression for the evaluation of public health interventions: a tutorial

Abstract: Interrupted time series (ITS) analysis is a valuable study design for evaluating the effectiveness of population-level health interventions that have been implemented at a clearly defined point in time. It is increasingly being used to evaluate the effectiveness of interventions ranging from clinical therapy to national public health legislation. Whereas the design shares many properties of regression-based approaches in other epidemiological studies, there are a range of unique features of time series data that require additional methodological considerations. In this tutorial we use a worked example to demonstrate a robust approach to ITS analysis using segmented regression. We begin by describing the design and considering when ITS is an appropriate design choice. We then discuss the essential, yet often omitted, step of proposing the impact model a priori. Subsequently, we demonstrate the approach to statistical analysis including the main segmented regression model. Finally we describe the main methodological issues associated with ITS analysis: over-dispersion of time series data, autocorrelation, adjusting for seasonal trends and controlling for time-varying confounders, and we also outline some of the more complex design adaptations that can be used to strengthen the basic ITS design.

Cohort Profile: The National Health Insurance Service–National Sample Cohort (NHIS-NSC), South Korea

Abstract: Cohort Profile: The National Health Insurance Service–National Sample Cohort (NHIS-NSC), South Korea Juneyoung Lee, Ji Sung Lee, Sook-Hee Park, Soon Ae Shin and KeeWhan Kim* Department of Biostatistics, College of Medicine, Korea University, Seoul, Korea, Clinical Research Center, Asian Medical Center, Seoul, Korea, Big Data Steering Department, National Health Insurance Service, Seoul, Korea and Department of Applied Statistics, Korea University Sejong Campus, Sejong City, Korea

Data Resource Profile: The Danish National Prescription Registry.

Abstract: Data Resource Profile: The Danish National Prescription Registry Anton Pottegård,* Sigrun Alba Johannesdottir Schmidt, Helle Wallach-Kildemoes, Henrik Toft Sørensen, Jesper Hallas and Morten Schmidt Clinical Pharmacology and Pharmacy, University of Southern Denmark, Odense, Denmark, Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark, Social and Clinical Pharmacy, University of Copenhagen, Copenhagen, Denmark and Department of Internal Medicine, Regional Hospital of Randers, Randers, Denmark

Data resource profile The national health information database of the national health insurance service in South Korea

Abstract: Seong, Sang Cheol; Kim, Yeon-Yong; Khang, Young-Ho; Park, Jong Heon; Kang, Hee-Jin; Lee, Heeyoung; Do, Cheol-Ho; Song, Jong-Sun; Bang, Ji Hyon; Ha, Seongjun; Lee, Eun-Joo; Shin, Soon AeOctober, 2016Data resource profile,Articles,[Wentworthville, Australia]International Epidemiological Association,6

Assessing the suitability of summary data for two-sample Mendelian randomization analyses using MR-Egger regression: the role of the I2 statistic

Abstract: Background: MR-Egger regression has recently been proposed as a method for Mendelian randomization (MR) analyses incorporating summary data estimates of causal effect from multiple individual variants, which is robust to invalid instruments. It can be used to test for directional pleiotropy and provides an estimate of the causal effect adjusted for its presence. MR-Egger regression provides a useful additional sensitivity analysis to the standard inverse variance weighted (IVW) approach that assumes all variants are valid instruments. Both methods use weights that consider the single nucleotide polymorphism (SNP)-exposure associations to be known, rather than estimated. We call this the `NO Measurement Error' (NOME) assumption. Causal effect estimates from the IVW approach exhibit weak instrument bias whenever the genetic variants utilized violate the NOME assumption, which can be reliably measured using the F-statistic. The effect of NOME violation on MR-Egger regression has yet to be studied. Methods: An adaptation of the I2 statistic from the field of meta-analysis is proposed to quantify the strength of NOME violation for MR-Egger. It lies between 0 and 1, and indicates the expected relative bias (or dilution) of the MR-Egger causal estimate in the two-sample MR context. We call it IGX2. The method of simulation extrapolation is also explored to counteract the dilution. Their joint utility is evaluated using simulated data and applied to a real MR example. Results: In simulated two-sample MR analyses we show that, when a causal effect exists, the MR-Egger estimate of causal effect is biased towards the null when NOME is violated, and the stronger the violation (as indicated by lower values of IGX2), the stronger the dilution. When additionally all genetic variants are valid instruments, the type I error rate of the MR-Egger test for pleiotropy is inflated and the causal effect underestimated. Simulation extrapolation is shown to substantially mitigate these adverse effects. We demonstrate our proposed approach for a two-sample summary data MR analysis to estimate the causal effect of low-density lipoprotein on heart disease risk. A high value of IGX2 close to 1 indicates that dilution does not materially affect the standard MR-Egger analyses for these data. Conclusions: Care must be taken to assess the NOME assumption via the IGX2 statistic before implementing standard MR-Egger regression in the two-sample summary data context. If IGX2 is sufficiently low (less than 90%), inferences from the method should be interpreted with caution and adjustment methods considered.

Cohort Profile Update: The Norwegian Mother and Child Cohort Study (MoBa)

Abstract: This is an update of the Norwegian Mother and Child Cohort Study (MoBa) cohort profile which was published in 2006. Pregnant women attending a routine ultrasound examination were initially invited. The first child was born in October 1999 and the last in July 2009. The participation rate was 41%. The cohort includes more than 114 000 children, 95 000 mothers and 75 000 fathers. About 1900 pairs of twins have been born. There are approximately 16 400 women who participate with more than one pregnancy. Blood samples were obtained from both parents during pregnancy and from mothers and children (umbilical cord) after birth. Samples of DNA, RNA, whole blood, plasma and urine are stored in a biobank. During pregnancy, the mother responded to three questionnaires and the father to one. After birth, questionnaires were sent out when the child was 6 months, 18 months and 3 years old. Several sub-projects have selected participants for in-depth clinical assessment and exposure measures. The purpose of this update is to explain and describe new additions to the data collection, including questionnaires at 5, 7, 8 and 13 years as well as linkages to health registries, and to point to some findings and new areas of research. Further information can be found at [www.fhi.no/moba-en]. Researchers interested in collaboration and access to the data can complete an electronic application available on the MoBa website above.

Commentary: Two-sample Mendelian randomization: opportunities and challenges.

Abstract: In this volume of the IJE , Gao and colleagues explore the causal effect of adiposity on several cancers using two-sample Mendelian randomization (MR), and find some evidence that greater adult body mass index (BMI) causally reduces the risk of breast cancer while increasing ovarian, lung and colorectal cancer. 1 The authors conclude that the study provides ‘…additional understanding of the complex relationship between adiposity and cancer risks’. Beyond the study findings themselves, this paper is interesting in its use of publicly available genome-wide association study (GWAS) summary data in a two-sample MR approach. Whereas MR has been increasingly used over the past decade since it was first proposed in the IJE , 2 two-sample MR is a relatively recent extension. 3 With the increasing availability of complete summary results from GWAS consortia that are easily accessible on the internet, the use of two-sample MR is likely to increase considerably over the next decade. 4 By complete summary data I mean results for all genetic loci with a trait or disease outcome, and not just those reaching a pre-specified P -value threshold as shown in journal publications. It is this extensive availability of results that allows Gao et al. to relate genetic variants used as instrumental variables for adiposity traits to the cancer outcomes that they are interested in; the published GWAS for the cancer outcomes would not have reported on the adiposity variants unless they reached a pre-specified GWAS significance value.

Two-sample Mendelian randomization: avoiding the downsides of a powerful, widely applicable but potentially fallible technique.

Abstract: Two-sample Mendelian randomization: avoiding the downsides of a powerful, widely applicable but potentially fallible technique Fernando Pires Hartwig*, Neil Martin Davies, Gibran Hemani and George Davey Smith Postgraduate Program in Epidemiology, Federal University of Pelotas, Pelotas, Brazil, Medical Research Council Integrative Epidemiology Unit at the University of Bristol and School of Social and Community Medicine, University of Bristol, Bristol, UK

Causality and causal inference in epidemiology: the need for a pluralistic approach.

Abstract: Causal inference based on a restricted version of the potential outcomes approach reasoning is assuming an increasingly prominent place in the teaching and practice of epidemiology. The proposed concepts and methods are useful for particular problems, but it would be of concern if the theory and practice of the complete field of epidemiology were to become restricted to this single approach to causal inference. Our concerns are that this theory restricts the questions that epidemiologists may ask and the study designs that they may consider. It also restricts the evidence that may be considered acceptable to assess causality, and thereby the evidence that may be considered acceptable for scientific and public health decision making. These restrictions are based on a particular conceptual framework for thinking about causality. In Section 1, we describe the characteristics of the restricted potential outcomes approach (RPOA) and show that there is a methodological movement which advocates these principles, not just for solving particular problems, but as ideals for which epidemiology as a whole should strive. In Section 2, we seek to show that the limitation of epidemiology to one particular view of the nature of causality is problematic. In Section 3, we argue that the RPOA is also problematic with regard to the assessment of causality. We argue that it threatens to restrict study design choice, to wrongly discredit the results of types of observational studies that have been very useful in the past and to damage the teaching of epidemiological reasoning. Finally, in Section 4 we set out what we regard as a more reasonable 'working hypothesis' as to the nature of causality and its assessment: pragmatic pluralism.

Effect of personalized nutrition on health-related behaviour change: evidence from the Food4me European randomized controlled trial

Abstract: This is a pre-copyedited, author-produced version of an article accepted for publication in International Journal of Epidemiology following peer review. The version of record [Carlos Celis-Morales, et al, 'Effect of personalized nutrition on health-related behaviour change: evidence from the Food4Me European randomized controlled trail', International Journal of Epidemiology, Vol. 46 (2): 578-588, August 2016] is available online at: https://academic.oup.com/ije/article-lookup/doi/10.1093/ije/dyw186.

The effects of waterpipe tobacco smoking on health outcomes: an updated systematic review and meta-analysis.

Abstract: Background and aims A systematic review conducted in 2008 found significant associations between waterpipe tobacco smoking and lung cancer, respiratory disease, periodontal disease and low birthweight. Since then, a number of relevant studies have been published. The objective of this study was to update the systematic review on the effects of waterpipe tobacco smoking on health outcomes. Methods In May 2015 we electronically searched the following databases with no date restrictions: MEDLINE, EMBASE and the ISI Web of Science using a detailed search strategy with no language restrictions. We also screened the references' lists of the included studies. We included cohort, case-control and cross-sectional studies, and excluded case reports, conference abstracts, editorials and reviews. We excluded studies not conducted in humans, assessing physiological outcomes, not distinguishing waterpipe tobacco smoking from other forms of smoking or not reporting association measures. We assessed risk of bias for each included study and conducted meta-analyses for each of the outcomes of interest. Results We identified 50 eligible studies. We found that waterpipe tobacco smoking was significantly associated with: respiratory diseases [COPD; odds ratio (OR) = 3.18, 95% confidence interval CI = 1.25, 8.08; bronchitis OR = 2.37, 95% CI = 1.49, 3.77; passive waterpipe smoking and wheeze OR) = 1.97, 95% CI = 1.28, 3.04]; oral cancer OR = 4.17, 95% CI = 2.53, 6.89; lung cancer OR = 2.12, 95% CI = 1.32, 3.42; low birthweight (OR = 2.39, 95% CI = 1.32, 4.32); metabolic syndrome (OR 1.63-1.95, 95% CI = 1.25, 2.45); cardiovascular disease (OR = 1.67, 95% CI = 1.25, 2.24); and mental health (OR 1.30-2.4, 95% CI = 1.20, 2.80). Waterpipe tobacco smoking was not significantly associated with: oesophageal cancer (OR = 4.14, 95% CI = 0.93, 18.46); worse quality of life scores [standardized mean difference (SMD) = -0.16, 95% CI = -0.66, 0.34]; gastric carcinoma (OR = 2.16, 95% CI = 0.72, 6.47); bladder cancer (OR = 1.25, 95% CI = 0.99, 1.57); prostate cancer (OR = 7.00, 95% CI = 0.90, 56.90); hepatitis C infection (OR = 0.98, 95%0.80, 1.21); periodontal disease (OR = 3.00, 5.00); gastro-oesophageal reflux disease (OR = 1.25, 95% CI = 1.01, 1.56); nasopharyngeal carcinoma (OR = 0.49, 95% CI = 0.20, 1.23); bladder cancer (OR = 1.25, 95% CI = 0.99, 1.57); infertility (OR = 2.50, 95% CI = 1.00, 6.30); and mortality (OR = 1.15, 95% CI = 0.93, 1.43). Conclusions There is accumulating evidence about the association of waterpipe tobacco smoking with a growing number of health outcomes.

Child marriage and intimate partner violence: a comparative study of 34 countries.

Abstract: Background : Studies in South Asia suggest that child marriage is a strong risk factor for intimate partner violence (IPV), but evidence outside the region is lacking. Methods : This study uses standardized data from demographic and health surveys in 34 countries to test the hypothesis that young women (age 20-24) who married as children are at increased risk of past year physical and/or sexual IPV as compared with those women who married as adults. Results : Globally, 9% of respondents were married before they turned 15; another 25% were married between the ages of 15 and 17. Past year physical and/or sexual IPV was higher among women who married as children (29%) compared with those who married as adults (20%). This difference persisted in logistic regression models that adjust for sociodemographic characteristics [odds ratio (OR) 1.41 (1.30-1.52) for marriage before 15, and 1.42 (1.35-1.50) for marriage at 15-17]. However, there was considerable heterogeneity between countries: marriage before age 15 was associated with a combined measure of past year physical and/or sexual IPV in nine countries; women married between 15 and 17 were at increased risk of physical and/or sexual IPV in 19 countries. This heterogeneity was most evident in sub-Saharan Africa, and warrants further investigation in so far as it may help identify protective policies and norms. Conclusion : Substantial reductions in IPV will likely require interventions to combat child marriage itself and to protect women from IPV within child marriages.

Variation in worldwide incidence of amyotrophic lateral sclerosis: a meta-analysis

Abstract: To assess the worldwide variation of amyotrophic lateral sclerosis (ALS) incidence, we performed a systematic review and meta-analysis of population-based data published to date. We reviewed Medline and Embase up to June 2015 and included all population-based studies of newly diagnosed ALS cases, using multiple sources for case ascertainment. ALS crude and standardized incidence (on age and sex using the US 2010 population) were calculated. Random effect meta-analysis and meta-regression were performed using the subcontinent as the main study level covariate. Sources of heterogeneity related to the characteristics of the study population and the study methodology were investigated. Among 3216 records, 44 studies were selected, covering 45 geographical areas in 11 sub-continents. A total of 13 146 ALS cases and 825 million person-years of follow-up (PYFU) were considered. The overall pooled worldwide crude ALS incidence was at 1.75 (1.55-1.96)/100 000 PYFU; 1.68 (1.50-1.85)/100 000 PYFU after standardization. Heterogeneity was identified in ALS standardized incidence between North Europe [1.89 (1.46-2.32)/100 000 PYFU] and East Asia [0.83 (0.42-1.24)/100 000 PYFU, China and Japan P = 0.001] or South Asia [0.73 (0.58-0.89)/100 000/PYFU Iran, P = 0.02]. Conversely, homogeneous rates have been reported in populations from Europe, North America and New Zealand [pooled ALS standardized incidence of 1.81 (1.66-1.97)/100 000 PYFU for those areas]. This review confirms a heterogeneous distribution worldwide of ALS, and sets the scene to sustain a collaborative study involving a wide international consortium to investigate the link between ancestry, environment and ALS incidence.

The epigenetic clock and telomere length are independently associated with chronological age and mortality

Abstract: Telomere length and DNA methylation have been proposed as biological clock measures that track chronological age. Whether they change in tandem, or contribute independently to the prediction of chronological age, is not known.

An introduction to multiplicity issues in clinical trials: the what, why, when and how.

Abstract: In clinical trials it is not uncommon to face a multiple testing problem which can have an impact on both type I and type II error rates, leading to inappropriate interpretation of trial results. Multiplicity issues may need to be considered at the design, analysis and interpretation stages of a trial. The proportion of trial reports not adequately correcting for multiple testing remains substantial. The purpose of this article is to provide an introduction to multiple testing issues in clinical trials, and to reduce confusion around the need for multiplicity adjustments. We use a tutorial, question-and-answer approach to address the key issues of why, when and how to consider multiplicity adjustments in trials. We summarize the relevant circumstances under which multiplicity adjustments ought to be considered, as well as options for carrying out multiplicity adjustments in terms of trial design factors including Population, Intervention/Comparison, Outcome, Time frame and Analysis (PICOTA). Results are presented in an easy-to-use table and flow diagrams. Confusion about multiplicity issues can be reduced or avoided by considering the potential impact of multiplicity on type I and II errors and, if necessary pre-specifying statistical approaches to either avoid or adjust for multiplicity in the trial protocol or analysis plan.

International trends in anal cancer incidence rates.

Abstract: Background Previous studies have reported rapid increases in anal cancer incidence rates in seven high-income countries in North America, Europe and Oceania There is very limited information on whether this pattern is replicated in other parts of the world In this study, we examine recent trends in anal cancer incidence in 18 countries worldwide Methods We calculated age-standardized incidence rates for anal squamous cell carcinoma (ASCC) and anal adenocarcinoma (AAC) for a minimum of 13 years through to 2007, using data from the International Agency for Research on Cancer's Cancer Incidence in Five Continents series, and applied joinpoint regression models to assess changes in incidence rates We also conducted an extended analysis of the data from the USA through to 2012 Results ASCC was the main histological subtype in most of the countries considered in this analysis The incidence of ASCC increased in both men and women in several high-income countries, including Australia, Canada, Denmark, France, Italy, Netherlands, the UK and the USA, whereas it increased only in women in Colombia, Estonia, the Russian Federation, Slovakia and Switzerland Conversely, there was little change in the incidence of ASCC in either men or women in India, Israel, Japan, Singapore and Spain The incidence rates of AAC decreased or were stable in most populations Conclusions The ASCC incidence rates increased in both men and women or in women in all countries included in this study, except Asian countries and Spain, where the rates remained unchanged Population-based preventive measures, including human papillomavirus vaccination and advocacy for safe sexual behaviours, may contribute to curbing the surging burden of the disease

Selecting instruments for Mendelian randomization in the wake of genome-wide association studies

Abstract: Mendelian randomization (MR) studies typically assess the pathogenic relevance of environmental exposures or disease biomarkers, using genetic variants that instrument these exposures. The approach is gaining popularity-our systematic review reveals a greater than 10-fold increase in MR studies published between 2004 and 2015. When the MR paradigm was first proposed, few biomarker- or exposure-related genetic variants were known, most having been identified by candidate gene studies. However, genome-wide association studies (GWAS) are now providing a rich source of potential instruments for MR analysis. Many early reviews covering the concept, applications and analytical aspects of the MR technique preceded the surge in GWAS, and thus the question of how best to select instruments for MR studies from the now extensive pool of available variants has received insufficient attention. Here we focus on the most common category of MR studies-those concerning disease biomarkers. We consider how the selection of instruments for MR analysis from GWAS requires consideration of: the assumptions underlying the MR approach; the biology of the biomarker; the genome-wide distribution, frequency and effect size of biomarker-associated variants (the genetic architecture); and the specificity of the genetic associations. Based on this, we develop guidance that may help investigators to plan and readers interpret MR studies.

Cohort Profile: The EDEN mother-child cohort on the prenatal and early postnatal determinants of child health and development

Abstract: The overall objective of the EDEN study was to examine the relations and potential interactions between maternal exposures and health status during pregnancy, fetal development, health status of the infant at birth and the child's health and development.

Outcome modelling strategies in epidemiology: traditional methods and basic alternatives.

Abstract: Controlling for too many potential confounders can lead to or aggravate problems of data sparsity or multicollinearity, particularly when the number of covariates is large in relation to the study size. As a result, methods to reduce the number of modelled covariates are often deployed. We review several traditional modelling strategies, including stepwise regression and the 'change-in-estimate' (CIE) approach to deciding which potential confounders to include in an outcome-regression model for estimating effects of a targeted exposure. We discuss their shortcomings, and then provide some basic alternatives and refinements that do not require special macros or programming. Throughout, we assume the main goal is to derive the most accurate effect estimates obtainable from the data and commercial software. Allowing that most users must stay within standard software packages, this goal can be roughly approximated using basic methods to assess, and thereby minimize, mean squared error (MSE).

The last two decades of life course epidemiology, and its relevance for research on ageing.

Abstract: The term ‘life course epidemiology’ was coined in 1997 with the publication of the first edition of A Life Course Approach to Chronic Disease Epidemiology.1 This book reviewed the pre-adult risk factors for cardiometabolic and respiratory disease, the catalyst being the imaginative research on the fetal origins of adult disease being driven forward at that time by Professor David Barker. We defined life course epidemiology as ‘the study of long-term biological, behavioural and psychosocial processes that link adult health and disease risk to physical or social exposures acting during gestation, childhood, adolescence, earlier in adult life or across generations’.1 Although our definition of life course epidemiology has stood the test of time, the field has evolved and there have been conceptual developments, methodological innovations which facilitate efforts to test these concepts, and an increasing corpus of empirical research demonstrating how factors from earlier life are associated with later life health and disease, as well as the pathways and biological mechanisms that may be involved. These developments have generated further ideas and challenges to life course models in an iterative process. As the theme of this special issue suggests, one important development has been the gradual shift of research focus from clinical disease endpoints to multi-faceted traits and longitudinal trajectories of functional phenotypes that can be assessed well before any clinical threshold is reached. This has naturally led on to the application of a life course epidemiological approach to ageing. The purpose of this overview is therefore to assess the development and current state of the field of life course epidemiology, including its recent application to the study of ageing as the focus of this special issue.

Bicycle injuries and helmet use: a systematic review and meta-analysis.

Abstract: BACKGROUND: The research literature was systematically reviewed and results were summarized from studies assessing bicycle helmet effectiveness to mitigate head, serious head, face, neck and fatal head injury in a crash or fall. METHODS: Four electronic databases (MEDLINE, EMBASE, COMPENDEX and SCOPUS) were searched for relevant, peer-reviewed articles in English. Included studies reported medically diagnosed head, face and neck injuries where helmet use was known. Non-approved helmets were excluded where possible. Summary odds ratios (OR) were obtained using multivariate meta-regression models stratified by injury type and severity. Time trends and publication bias were assessed. RESULTS: A total of 43 studies met inclusion criteria and 40 studies were included in the meta-analysis with data from over 64 000 injured cyclists. For cyclists involved in a crash or fall, helmet use was associated with odds reductions for head [OR = 0.49, 95% confidence interval (CI): 0.42-0.57), serious head (OR = 0.31, 95% CI: 0.25-0.37), face (OR = 0.67, 95% CI: 0.56-0.81) and fatal head injury (OR = 0.35, 95% CI: 0.14-0.88). No clear evidence of an association between helmet use and neck injury was found (OR = 0.96, 95% CI: 0.74-1.25). There was no evidence of time trends or publication bias. CONCLUSIONS: Bicycle helmet use was associated with reduced odds of head injury, serious head injury, facial injury and fatal head injury. The reduction was greater for serious or fatal head injury. Neck injury was rare and not associated with helmet use. These results support the use of strategies to increase the uptake of bicycle helmets as part of a comprehensive cycling safety plan.© The Author 2016; all rights reserved. Published by Oxford University Press on behalf of the International Epidemiological Association. Language: en

An introduction to g methods

Abstract: Robins' generalized methods (g methods) provide consistent estimates of contrasts (e.g. differences, ratios) of potential outcomes under a less restrictive set of identification conditions than do standard regression methods (e.g. linear, logistic, Cox regression). Uptake of g methods by epidemiologists has been hampered by limitations in understanding both conceptual and technical details. We present a simple worked example that illustrates basic concepts, while minimizing technical complications.

The tale wagged by the DAG: broadening the scope of causal inference and explanation for epidemiology.

Abstract: 'Causal inference', in 21st century epidemiology, has notably come to stand for a specific approach, one focused primarily on counterfactual and potential outcome reasoning and using particular representations, such as directed acyclic graphs (DAGs) and Bayesian causal nets. In this essay, we suggest that in epidemiology no one causal approach should drive the questions asked or delimit what counts as useful evidence. Robust causal inference instead comprises a complex narrative, created by scientists appraising, from diverse perspectives, different strands of evidence produced by myriad methods. DAGs can of course be useful, but should not alone wag the causal tale. To make our case, we first address key conceptual issues, after which we offer several concrete examples illustrating how the newly favoured methods, despite their strengths, can also: (i) limit who and what may be deemed a 'cause', thereby narrowing the scope of the field; and (ii) lead to erroneous causal inference, especially if key biological and social assumptions about parameters are poorly conceived, thereby potentially causing harm. As an alternative, we propose that the field of epidemiology consider judicious use of the broad and flexible framework of 'inference to the best explanation', an approach perhaps best developed by Peter Lipton, a philosopher of science who frequently employed epidemiologically relevant examples. This stance requires not only that we be open to being pluralists about both causation and evidence but also that we rise to the challenge of forging explanations that, in Lipton's words, aspire to 'scope, precision, mechanism, unification and simplicity'.

Social relationships and cognitive decline: a systematic review and meta-analysis of longitudinal cohort studies

Abstract: Background: Although poor social relationships are assumed to contribute to cognitive decline, meta-analytic approaches have not been applied. Individual study results are mixed and difficult to interpret due to heterogeneity in measures of social relationships. We conducted a systematic review and meta-analysis to investigate the relation between poor social relationships and cognitive decline. Methods: MEDLINE, Embase and PsycINFO were searched for longitudinal cohort studies examining various aspects of social relationships and cognitive decline in the general population. Odds ratios (ORs) with 95% confidence intervals (CIs) were pooled using random effects meta-analysis. Sources of heterogeneity were explored and likelihood of publication bias was assessed. We stratified analyses according to three aspects of social relationships: structural, functional and a combination of these. Results: We identified 43 articles. Poor social relationships predicted cognitive decline; for structural (19 studies): pooled OR: 1.08 (95% CI: 1.05-1.11); functional (8 studies): pooled OR: 1.15 (95% CI: 1.00-1.32); and combined measures (7 studies): pooled OR: 1.12 (95% CI: 1.01-1.24). Meta-regression and subgroup analyses showed that the heterogeneity could be explained by the type of social relationship measurement and methodological quality of included studies. Conclusions: Despite heterogeneity in study design and measures, our meta-analyses show that multiple aspects of social relationships are associated with cognitive decline.As evidence for publication bias was found, the association might be overestimated and should therefore be interpreted with caution. Future studies are needed to better define the mechanisms underlying these associations. Potential causality of this prognostic association should be examined in future randomized controlled studies.

What should we know about precarious employment and health in 2025? framing the agenda for the next decade of research

Abstract: The generalization of flexible labour markets, the declining influence of unions and the degradation of social protection has led to the emergence of new forms of employment at the expense of the Standard Employment Relationship, as well as a considerable amount of research across social and scientific disciplines. Years ago we suggested the urgent need to disentangle the consequences of new types of employment for the health and well-being of workers, contending that the study of precarious employment and health is in its infancy. Today, research challenges include clearer, more precise definitions of the original concepts, a more detailed understanding of the pathways and mechanisms through which precarious employment harms worker health, stronger information systems for monitoring the problem and a complex systems approach to employment conditions and health research. All of these must be guided by the theoretical and policy debates linking precarious employment and health, and be geared towards developing better tools for the design, implementation and evaluation of policies intended to minimize precariousness in the labour market and its effects on public health and health inequalities. Our aim in this paper is to outline an agenda for the next decade of research on precarious employment and health, establishing a compelling programme that expands our understanding of complex causes and links.

Quantified relations between exposure to tobacco smoking and bladder cancer risk: a meta-analysis of 89 observational studies

Abstract: BACKGROUND Smoking is a major risk factor for bladder cancer (BC). This meta-analysis updates previous reviews on smoking characteristics and BC risk, and provides a more quantitative estimation of the dose-response relationship between smoking characteristics and BC risk. METHODS In total, 89 studies comprising data from 57 145 BC cases were included and summary odds ratios (SORs) were calculated. Dose-response meta-analyses modelled relationships between smoking intensity, duration, pack-years and cessation and BC risk. Sources of heterogeneity were explored and sensitivity analyses were conducted to test the robustness of findings. RESULTS Current smokers (SOR = 3.14, 95% CI = 2.53-3.75) and former smokers(SOR = 1.83, 95% CI = 1.52-2.14) had an increased risk of BC compared with never smokers. Age at first exposure was negatively associated with BC risk. BC risk increased gradually by smoking duration and a risk plateau at smoking 15 cigarettes a day and 50 pack-years was observed. Smoking cessation is most beneficial from 20 years before diagnosis. The population-attributable risk of BC for smokers has decreased from 50% to 43% in men and from 35% to 26% in women from Europe since estimated in 2000. Results were homogeneous between sources of heterogeneity, except for lower risk estimates found in studies of Asian populations. CONCLUSIONS Active smokers are at an increased risk of BC. Dose-response meta-analyses showed a BC risk plateau for smoking intensity and indicate that even after long-term smoking cessation, an elevated risk of bladder cancer remains.

The effects of age on crash risk associated with driver distraction.

Abstract: BACKGROUND: Driver distraction is a major contributing factor to crashes, which are the leading cause of death for the US population under 35 years of age. The prevalence of secondary-task engagement and its impacts on distraction and crashes may vary substantially by driver age. Methods: Driving performance and behaviour data were collected continuously using multiple cameras and sensors in situ for 3542 participant drivers recruited for up to 3 years for the Second Strategic Highway Research Program Naturalistic Driving Study. Secondary-task engagement at the onset of crashes and during normal driving segments was identified from videos. A case-cohort approach was used to estimate the crash odds ratios associated with, and the prevalence of, secondary tasks for four age groups: 16-20, 21-29, 30-64 and 65-98 years of age. Only severe crashes (property damage and higher severity) were included in the analysis. Results: Secondary-task-induced distraction posed a consistently higher threat for drivers younger than 30 and above 65 when compared with middle-aged drivers, although senior drivers engaged in secondary tasks much less frequently than their younger counterparts. Secondary tasks with high visual-manual demand (e.g. visual-manual tasks performed on cell phones) affected drivers of all ages. Certain secondary tasks, such as operation of in-vehicle devices and talking/singing, increased the risk for only certain age groups. Conclusions: Teenaged, young adult drivers and senior drivers are more adversely impacted by secondary-task engagement than middle-aged drivers. Visual-manual distractions impact drivers of all ages, whereas cognitive distraction may have a larger impact on young drivers. Language: en

Probabilistic record linkage

Abstract: Studies involving the use of probabilistic record linkage are becoming increasingly common. However, the methods underpinning probabilistic record linkage are not widely taught or understood, and therefore these studies can appear to be a 'black box' research tool. In this article, we aim to describe the process of probabilistic record linkage through a simple exemplar. We first introduce the concept of deterministic linkage and contrast this with probabilistic linkage. We illustrate each step of the process using a simple exemplar and describe the data structure required to perform a probabilistic linkage. We describe the process of calculating and interpreting matched weights and how to convert matched weights into posterior probabilities of a match using Bayes theorem. We conclude this article with a brief discussion of some of the computational demands of record linkage, how you might assess the quality of your linkage algorithm, and how epidemiologists can maximize the value of their record-linked research using robust record linkage methods.

Data Resource Profile: The Korea Youth Risk Behavior Web-based Survey (KYRBS)

Abstract: Data Resource Profile: The Korea Youth Risk Behavior Web-based Survey (KYRBS) Yoonjung Kim, Sunhye Choi, Chaemin Chun, Suyeon Park, Young-Ho Khang and Kyungwon Oh* Division of Health and Nutrition Survey, Centers for Disease Control and Prevention, Cheongju-si, Korea, Department of Health Policy and Management, Seoul National University College of Medicine, Seoul, Korea and Institute of Health Policy and Management, Seoul National University Medical Research Center, Seoul, Korea