Citation of updated and co-published Cochrane Methodology Reviews

To evaluate the number of citations for Cochrane Methodology Reviews after they have been updated or co-published in another journal, and the effect of co-publishing the review on the co-publishing journal's impact factor (IF). We identified all Cochrane Methodology Reviews published in the Cochrane Database of Systematic Reviews (CDSR) before 2018 and searched for co-published versions in the Web of Science Core Collection database up to 16 August 2022. The included reviews were in two cohorts: those that had been published and updated in CDSR and those that had been published in CDSR and co-published in another journal. The primary outcome measured the citation number to updated and original reviews in the first five years after publication of the updated review, and assessed the citation number of co-published and non-co-published reviews in the first five years after publication of the co-published version. The secondary outcome was the ratio of an adjusted IF and the actual IF of the co-publishing journal. Eight updated and six original reviews were identified for the updated cohort of reviews, and four co-published reviews were included in the co-published cohort. The original reviews continued to be cited after the update was published but the median for the total number of citations was non-significantly higher for the updated reviews than for their original version[161 (Interquartile range (IQR) 85, 198) versus 113 (IQR 15, 433)]. The median number of total citations [362 (IQR 179, 840) versus 145 (IQR 75, 445)] and the median number of citations to the review in the first five years after co-publication combined and in each of those years was higher in the co-published group than in the non-co-published group. One of the three journals that co-published Reviews in the first year and two journals in the second year had a lower IF after co-publication. Earlier versions of Cochrane Methodology Reviews continue to be cited after an update is published, which raises doubts about whether those citing are using the most recent evidence or are aware of the update. Co-publication facilitates broader application and dissemination of Cochrane methodology evidence.