Statistical methods can be improved within Cochrane pregnancy and childbirth reviews.
OBJECTIVE
To assess statistical methods within systematic reviews of the Cochrane Pregnancy and Childbirth Group (CPCG).


METHODS
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.


CONCLUSIONS
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.
Department of Public Health, Epidemiology and Biostatistics, Public Health Building, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. r.d.riley@bham.ac.uk
Richard D
RD
Riley
Simon
S
Gates
James
J
Neilson
Zarko
Z
Alfirevic
D005260:Female; D006801:Humans; D015201:Meta-Analysis as Topic; D036801:Parturition; D011247:Pregnancy; D017594:Publication Bias; D016032:Randomized Controlled Trials as Topic; D012196:Review Literature as Topic; D013223:Statistics as Topic / Q000592:standards*