Investigation of reporting bias in interrupted time series (ITS) studies: a study protocol

Abstract

Background Systematic reviews that aim to synthesize evidence on the effects of interventions targeted at populations often include interrupted time-series (ITS) studies. However, the suppression of ITS studies or results within these studies (known as reporting bias) has the potential to bias conclusions drawn in such systematic reviews, with potential consequences for healthcare decision-making. Therefore, we aim to determine whether there is evidence of reporting bias among ITS studies. Methods We will conduct a search for published protocols of ITS studies and reports of their results in PubMed, MEDLINE, and Embase up to December 31, 2022. We contact the authors of the ITS studies to seek information about their study, including submission status, data for unpublished results, and reasons for non-publication or non-reporting of certain outcomes. We will examine if there is evidence of publication bias by examining whether time-to-publication is influenced by the statistical significance of the study’s results for the primary research question using Cox proportional hazards regression. We will examine whether there is evidence of discrepancies in outcomes by comparing those specified in the protocols with those in the reports of results, and we will examine whether the statistical significance of an outcome’s result is associated with how completely that result is reported using multivariable logistic regression. Finally, we will examine discrepancies between protocols and reports of results in the methods by examining the data collection processes, model characteristics, and statistical analysis methods. Discrepancies will be summarized using descriptive statistics. Discussion These findings will inform systematic reviewers and policymakers about the extent of reporting biases and may inform the development of mechanisms to reduce such biases.