Ten studies (3,915 participants, range 71 to 1,012) were included in the review. Four studies were randomised and six were non-randomised. The mean and standard deviation Downs and Black score was 16±2. The main areas of poor scoring were insufficient explanation of and adjustment for main confounders, missing data and absence of description of source population.
Compared with rigid sigmoidoscopy, flexible sigmoidoscopy was associated with significantly higher rates of detection of colorectal cancer (RD 0.02, 95% CI 0.006 to 0.034; Ι²=69.6%) and any abnormality (RD 0.138, 95% CI 0.077 to 0.200; Ι²=94.7%). Both pooled estimates were based on nine studies.
Rigid sigmoidoscopy caused significantly more patient discomfort than flexible sigmoidoscopy (WMD 0.981 (95% CI 0.693 to 1.269; six studies; Ι²=92.9%).
Flexible sigmoidoscopy was associated with significantly greater depth of examination (SMD 3.175, 95% CI 2.397 to 3.954; nine studies; Ι²=99%). Compared with flexible sigmoidoscopy, rigid sigmoidoscopy was associated with significantly shorter examination times (SMD -1.601, 95% CI -2.728 to -0.474; six studies; Ι²=99%).
Separate pooled estimates for randomised and non-randomised studies were also reported.
The funnel plot suggested a limited possibility of publication bias.