Quality Control in Systematic Reviews and Meta-analyses

The numbers of publications each year from 1988 to 2008 with the words “systematic review” (grey bars) or “meta-analysis” (black bars) in the title. Data retrieved from ISI Web of Knowledge based on a search of MEDLINE^® (1950-present).

A forest plot of outcome data from a meta-analysis of 4 randomised trials of screening for Abdominal Aortic Aneurysm in men aged 64 to 83. Note the logarithmic scale and the vertical line at the threshold between outcome favouring treatment (in this case, screening) or control therapies. Reproduced with permission from: Lindholt JS. Norman P. Screening for abdominal aortic aneurysm reduces overall mortality in men. A meta-analysis of the mid- and long-term effects of screening for abdominal aortic aneurysms. European Journal of Vascular & Endovascular Surgery. 36(2):167–71, 2008.

a) A funnel plot demonstrating reasonable symmetry from a meta-analysis of 171 studies. b) A funnel plot demonstrating marked asymmetry (77 studies). In this case the outcome measure was intra-operative mortality and the missing studies that should occupy the lower right part of the funnel represent those with high intra-operative mortality rates. Both figures reproduced with permission from Bown MJ, Sutton AJ, Bell PR, Sayers RD. A meta-analysis of 50 years of ruptured abdominal aortic aneurysm repair. Br J Surg. 2002 Jun;89(6):714–30.