• Systematic review;
  • meta-analysis;
  • colorectal disease;
  • heterogeneity;
  • bias;
  • pitfalls


A systematic review (SR) is the unbiased appraisal of systematically identified relevant studies. Implicit in its definition is a robust and scientifically valid process, and when performed as such, SR is an important clinical research tool and influence in health policy decision-making. This educational paper outlines that, from the original prototype based on randomized trials, there are now many other types of SRs including those based on: nonrandomized comparative studies, observational studies, prognostic studies, and studies of diagnostic and screening tools. While each of these has a similar ‘anatomy’ or format, at an individual class level, there are principles specific to each SR type. Several examples from the coloproctology literature are used as case-studies to illustrate potential pitfalls, and upon re-analysis, often reverse or attenuate the conclusions stated in the original publication. These examples serve to emphasize the need for health professionals to understand the process of SR and meta-analysis so that we all arrive at appropriate interpretations to the benefit of our patients.