Abstract
BackgroundObservational studies are widely used in pharmacoepidemiology. Several designs can be used, in particular self-controlled designs (case-crossover and self-controlled case series). These designs offer the advantage of controlling for time-invariant confounders, which may not be collected in electronic healthcare databases. They are particularly useful in pharmacoepidemiology involving healthcare database. To be valid, they require the presence of some characteristics (key validity assumptions), and in such situations, these designs should be preferred. We aimed at describing the appropriate use and reporting of the key validity assumptions in self-controlled design studies.MethodsArticles published between January 2011 and December 2014, and describing a self-controlled study design involving electronic healthcare databases were retrieved. The appropriate use (fulfilment of key assumptions) was studied in terms of major (abrupt onset event, rare or recurrent event, and intermittent exposure) and minor assumptions (those for which the design can be adapted).ResultsAmong the 107 articles describing a self-controlled design, 35/53 (66%) case-crossover studies, and 48/55 (87%) self-controlled case series fulfilled the major validity assumptions for use of the design; 4/35 and 14/48 respectively did not fulfill the minor assumptions. Overall, 31/53 (58%) case-crossover studies and 34/55 (62%) self-controlled case series fulfilled both major and minor assumptions. The reporting of the methodology or the results was appropriate, except for power calculation.ConclusionsSelf-controlled designs were not appropriately used in34% and 13% of the articles we reviewed that described a case-crossover or a self-controlled case series design, respectively. We encourage better use of these designs in situations in which major validity assumptions are fulfilled (i.e., for which they are recommended), accounting for situations for which the design can be adapted.
Highlights
Observational studies are widely used in pharmacoepidemiology
18 (34%) articles using a case-crossover design and 7 (13%) articles using a self-controlled case series did not fulfil all of the major validity assumptions for their use: most frequently, the studies examined the effect of a sustained exposure, and 3 examined an event with an insidious onset
Among the 48 self-controlled case series with valid major assumptions, 14 did not fulfil the minor ones: 1 study examined an event with recurrences that were not independent, 6 studies violated the assumption of event-independent exposure and 8 studies examined an outcome that could censor the observation period
Summary
Several designs can be used, in particular self-controlled designs (case-crossover and self-controlled case series) These designs offer the advantage of controlling for time-invariant confounders, which may not be collected in electronic healthcare databases. Gault et al BMC Medical Research Methodology (2017) 17:25 status, alcohol consumption, or medical history and comorbidities) [2] In this context, in which many confounders may not be collected, self-controlled designs are an interesting option in observational studies of pharmaceuticals [5]. These designs have become applicable in more situations, by weakening the assumptions they require, such as the possibility to study time trend in exposure [14, 15], event-dependant exposure [16, 17], inter-dependant recurrences [18], or event-dependant observation periods [16, 19]
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