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)1904 321070 f: +44 (0)1904 321041 e: [email protected]

www.york.ac.uk/inst/crd

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