their contribution to knowledge Morag Heirs

Research Fellow Centre for Reviews and Dissemination University of York PhD student (NIHR funded) Health Sciences University of York t: +44 (0) f: +44 (0) e:

What is a systematic review Systematic Review Review of a clearly formulated question that uses explicit methods to minimise bias in the location, selection, critical evaluation and synthesis of research evidence. (may or may not involve quantitative synthesis) Meta-analysis Statistical techniques used to combine the results of two or more studies and obtain a pooled (combined) estimate of effect. (informative meta-analysis will usually also be a systematic review)

Traditional reviews ‘Unscientific’ rarely pre-specify or make methods explicit Usually subjective, opinions of individual Often incomplete, filing cabinet or MEDLINE review Difficult to make sense of conflicting or equivocal trials on qualitative reading alone

Why we need systematic reviews Synthesis Health care providers, researchers and policy makers are inundated with unmanageable amounts of information Need systematic reviews to summarise existing information and provide data for rational decision making Enable practitioners to keep up to date with evidence accumulating in field and to practice evidence-based medicine

Why we need systematic reviews Totality of evidence Evaluations and recommendations should be based on results of all trials not just published / well known trials that are likely to be biased towards positive (publication bias) Results of any one trial should be interpreted in the context of all relevant evidence consistency / inconsistency generalisability

Why we need systematic reviews Power and precision Often the benefits that can be expected of a new intervention are moderate These moderate benefits can be important clinically and in terms of public health Often trials recruit too few patients to detect such differences with reliability

Definitions and dilemmas Systematic reviews Are not restricted to including randomised controlled trials (RCTs) alone Do not always include meta-analysis (but should always provide a synthesis) Are a flexible and powerful methodology for answering a variety of questions

Appraising systematic reviews Adequate search Defined inclusion criteria – appropriate choices to answer the question Study selection/quality assessment/data extraction Avoidance of bias and error Synthesis (narrative, statistical, qualitative) taking into account quality of the primary studies

Conclusions Systematic reviews ≠ meta-analyses Systematic reviews ≠ only looking at RCTs Important to assess primary studies for risk of bias Quality assess the systematic review itself Systematic reviewing is a well established, adaptable methodology suitable for most topics and questions