Registration of observational studies of interventions: prevalence, author attitudes, and journal policies – a meta-research study

Prospective study registration is a key approach to mitigate reporting bias. Observational studies are not routinely registered. We aimed to estimate the prevalence of prospective registration among observational studies of health care interventions, explore authors’ attitudes toward registration, examine factors associated with prospective registration, and chart editorial policies on registration of observational studies in medical journals. We conducted a cross-sectional meta-research study comprising three components: 1) We sampled 200 PubMed-indexed cohort or case–control study publications assessing the effects of health care interventions, published in 2023, searched for corresponding publicly availably registration records, and surveyed the study authors on attitudes to registration; 2) We evaluated associations between prospective registration (≤ 1 month of study start) and study characteristics by multivariable logistic regression; 3) We examined editorial policies of 40 medical journals to identify requirements to register observational studies, and invited one editor per journal to share their perspectives on registration. We included 200 publications: 197 cohort studies and 3 case–control studies. In total, 17 (9%, 95% CI 5%-13%) were prospectively registered, and another 11 (6%, 95% CI 3%-10%) were retrospectively registered. Prospective registration was positively associated with having a publicly available protocol (adjusted OR 5.12, 95% CI 1.06–24.66; p = 0.042). Forty-six of 200 authors (23%) responded to the survey, of whom 60% supported registration. The authors perceived limited time and resources for the registration process (62%) and the absence of journal registration requirements (56%) as the main barriers. Of the 40 journal policies examined, none explicitly required registration of observational studies, while 12 (30%) encouraged it. Thirteen journal editors responded, of whom half considered registration of observational studies to be worthwhile. Approximately one in ten observational studies of interventions are prospectively registered. Authors perceive the lack of journal registration requirements as a key barrier to registering, and most examined journals do not require registration of observational studies. Given the increased reliance on observational studies of interventions when trials are unavailable, improved transparency measures are needed to reduce the risk of reporting bias.