A systematic review of the reporting and methodological quality of studies that use Mendelian randomisation in UK Biobank

BackgroundMendelian randomisation (MR) is a method of causal inference that uses genetic variation as an instrumental variable (IV) to account for confounding. While the number of MR articles published each year is rapidly rising (partly due to large cohort studies such as the UK Biobank making it easier to conduct MR), it is not currently known whether these studies are appropriately conducted and reported in enough detail for other researchers to accurately replicate and interpret them. MethodsWe conducted a systematic review of reporting and analysis quality of MR studies using only individual level data from the UK biobank to calculate a causal estimate. We reviewed 64 eligible articles on a 25-item checklist (based on the STROBE-MR reporting guidelines and the Guidelines for performing Mendelian Randomisation investigations). Information on article type and journal information was also extracted. ResultsOverall, the proportion of articles which reported complete information ranged from 2% to 100% across the different items. Palindromic variants, variant replication, missing data, associations between the IV and variables of exposure/outcome and bias introduced by two-sample methods used on a single sample were often not completely addressed (<11%). There was no clear evidence that Journal Impact Factor, word limit/recommendation or year of publication predicted percentage of article completeness (for the eligible analyses) across items, but there was evidence that whether the MR analyses were primary, joint-primary or secondary analyses did predict completeness. ConclusionsThe results identify areas in which the reporting and conducting of MR studies needs to be improved and highlights that this is independent of Journal Impact Factor, year of publication or word limits/recommendations.