Statistical methods can be improved within Cochrane pregnancy and childbirth reviews

Abstract

Objectives: To assess statistical methods within systematic reviews of the Cochrane Pregnancy and Childbirth Group (CPCG).

Study design and setting: We extracted details about statistical methods within 75 reviews containing at least 10 studies.

Results: The median number of forest plots per review was 52 (min=5; max=409). Seven of the 75 reviews assessed publication bias or explained why not. Forty-four of the 75 reviews performed random-effects meta-analyses; just 1 of these justified the approach clinically and none interpreted its pooled result correctly. Of 31 reviews not using random-effects, 26 assumed a fixed-effect given potentially moderate or large heterogeneity (I(2)>25%). In their Methods section, 25 (33%) of the 75 reviews said I(2) was used to decide between fixed-effect and random-effects; however, in 12 of these (48%) reviews, this was not carried out in their Results section. Of 72 reviews with moderate or large heterogeneity, 47 (65%) did not explore the causes of heterogeneity or justify why not.

Conclusion: Within CPCG reviews, publication bias is rarely addressed; heterogeneity is often not appropriately considered, and random-effects analyses are incorrectly interpreted. How these shortcomings impact existing review conclusions needs further investigation, but regardless of this, we recomment the Cochrane Collaboration increase "hands-on" statistical support.