Cochrane review abstracts are getting longer, but this has no large impact on the reporting quality

To evaluate the reporting of abstracts of Cochrane Reviews according to PRISMA-A and to investigate a possible association with the abstract´s length.

This is a retrospective, observational study based on all Cochrane Reviews indexed in Medline (via PubMed) until November 18, 2022. In the second part, a random sample of 440 abstracts was drawn, in which PRISMA-A adherence was assessed by two independent reviewers. Analyses were stratified by the year of publication and the number of words.

Overall, the median number of words of the 15,188 included abstracts was 469 (IQR 389-686 words), steadily increasing from 353 words in 2000 to 838 words in 2022, with less than one percent of the abstracts in 2022 having ≤ 300 words (in 2000: 30.7%). Analyses on PRISMA-A adherence in the random sample showed a mean score of 6.1 out of 12 fully reported items. Stratified by year, PRISMA-A adherence increased, with higher word counts in 2000-2010 and 2011-2015, while there was no difference in PRISMA-A adherence by abstract length in 2016-2022.

Over the years, abstracts of Cochrane Reviews have become longer, running up to 1000 words. This conflicts with the Cochrane Handbook, which recommends a maximum length of 400 until it was aligned with MECIR in 2019, which has recommended a length of <700 words since 2012 but allows up to 1000 words. It is debatable whether such long abstracts meet the key goals of abstracts of being informative, accurate, appealing, and concise.