A novel framework for classification of selection processes in epidemiological research
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(2020) 20:155
RESEARCH ARTICLE
Open Access
A novel framework for classification of selection processes in epidemiological research Jonas Björk1,2* , Anton Nilsson1,3, Carl Bonander4 and Ulf Strömberg4,5
Abstract 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. Keywords: Bias, Selection bias, Epidemiologic factors, Population characteristics, Public health
Background Selection and selection bias are terms that still lack consistent definitions in epidemiology, and they also have varying meaning and usage in other scientific disciplines [1, 2]. This is a source of misunderstandings that may compromise validity, not the least in the interdisciplinary collaborations that are common within empirical research today. Most definitions of selection bias in epidemiology restrict the attention to sample selection in * Correspondence: [email protected] 1 Division of Occupational and Environmental Medicine, Lund University, SE-221 85 Lund, Sweden 2 Clinical Studies Sweden, Forum South, Skåne University Hospital, Lund, Sweden Full list of author information is available at the end of the article
that selection is viewed as a bias-inducing phenomenon occurring at the study level, i.e. during design, enrolment, follow-up or analysis [3–5]. The focus on studyrelated issues when discussing selection bias implies that selection processes occurring at the population level, for example linked to migration, disease occurrence and mortality [6], are often overlooked among applied researchers. As an example of this narrow focus, it is sometimes claimed that selection bias is not an issue in cohort studies involving complete recruitment and follow-up [7]. There is also confusion in the literature between the underlying mechanisms that lead to selection and their consequences, i.
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