Conclusiveness of the Cochrane Eye and Vision Group Reviews

To assess the conclusiveness of Cochrane Eye and Vision Group Reviews (EVGRs). We tested the hypotheses that: (1) the majority of EVGRs are inconclusive; (2) most reviews state the need for further and better studies; (3) the conclusiveness of a given review is affected by the number of randomized controlled trials (RCTs) included and the cumulative number of patients and eyes studied.

A retrospective study of all EVGRs available in the Cochrane Library in June 2013. For each EVGR we recorded the number of RCTs found by the reviewers, the number of RCTs included for final analysis as fulfilling inclusion criteria, the total cumulative number of patients and eyes studied, the stated need for further and better studies, the reason stated for further studies and the type of conclusion reached by the reviewer(s). We used the Kruskal-Wallis test to determine differences between ''conclusive'' and ''inconclusive'' studies in terms of the outcome variables studied. The correlation between the number of included studies and cumulative sample size was studied using regression analysis.

Out of 106 EVGRs, 52.8% were conclusive. In 83.9% of the conclusive EVGRs one treatment/strategy/drug was found to be better than the alternative. The average number of available and included RCTs was significantly higher in conclusive EVGRs (P = 0.007 and P = 0.003 respectively). The total cumulative number of patients and number of eyes studied was approximately ten times higher in the conclusive EVGRs (P < 0.001 and P < 0.015 respectively). A similar percentage of RCTs was included in both conclusive and inconclusive reviews (76 vs. 73%). The vast majority of EVGRs, whether conclusive (84%) or inconclusive (96%), stated the need for further and better studies (P = 0.042). Fifty eight percent of the EVGRs justified the need for further studies for at least two reasons. The reason that was stated the most was a need for a larger amount of RCTs (67%).

In approximately half of the cases, EVGRs allow the reader to reach a clinically applicable conclusion. Larger total cumulative participants, total cumulative number of eyes studied and number of RCTs performed all increase the likelihood of an EVGR to be conclusive.