Abstract
Background: Prospectively registering study plans in a permanent time-stamped and publicly accessible document is becoming more common across disciplines and aims to improve the trustworthiness of research findings. Selective reporting persists, however, when researchers deviate from their registered plans without disclosure. This systematic review aims to estimate the prevalence of undisclosed discrepancies between prospectively registered study plans and their associated publication. We further aim to identify the research disciplines where these discrepancies have been observed, whether interventions to reduce discrepancies have been conducted, and gaps in the literature.
Methods: On 15 December 2019, we searched Scopus and Web of Knowledge for articles that included quantitative data about discrepancies between registrations or study protocols and their associated publications. We used random-effects meta-analyses to synthesize the results.
Results: We reviewed k = 89 articles, including k = 70 that report on primary outcome discrepancies from n = 6314 studies and, k = 22 that report on secondary outcome discrepancies from n = 1436 studies. Meta-analyses indicate that between 10% to 68% (95% prediction interval) of studies contain at least one primary outcome discrepancy and between 13% to 95% (95% prediction interval) contain at least one secondary outcome discrepancy. Almost all articles assessed clinical literature, and there was considerable heterogeneity, resulting in wide prediction intervals. We identified only one article that attempted to correct discrepancies.
Discussion: Many articles did not include information on whether discrepancies were disclosed, which version of a registration they compared publications to, and whether the registration was prospective. Thus, our estimates represent discrepancies broadly, rather than our target of undisclosed discrepancies between prospectively registered study plans and their associated publications. Discrepancies are common and reduce the trustworthiness of medical research. Interventions to reduce discrepancies could prove valuable.