MUSM Libraries: Evaluating a SYSTEMATIC REVIEW article
Size of treatment effect | Finding
Size of treatment effect
A systematic review is a concise summary of the best available
evidence that addresses a sharply defined clinical question.
A meta-analysis is a systematic review that uses quantitative
methods to summarize the results.
The test of homogeneity gauges whether it is reasonable to
combine the results of individual studies. It asks if the differences in
treatment effect from study to study are greater than one would expect as a
result of chance alone.
For meta-analyses of therapy, the results are interpreted as in for
articles of therapy:
Risk of Outcome: Y = a/(a+b)
Risk of Outcome: X =
- Absolute Risk Reduction (ARR) is the difference in risk
between the control group (X) and the treatment group (Y). ARR =
- Control Event Rate (CER)
The proportion of patients in the
control group who experience the studied event.
- Experimental Event Rate (EER)
The proportion of patients
in the experimental treatment group who are observed to experience the outcome
- Number Needed to Treat (NNT) is the number of patients that
must be treated over a given period of time to prevent one adverse outcome.
NNT = 1/ARR
- Odds Ratio (OR)
The ratio of the odds of having the target
disorder in the experimental group relative to the odds in favor of having the
target disorder in the control group (in cohort studies or systematic reviews)
or the odds in favor of being exposed in subjects with the target disorder
divided by the odds in favor of being exposed in control subjects (without the
- Relative Risk (RR) is the risk of the outcome in the treated
group (Y) compared to the risk in the control group. RR = Y/X
- Relative Risk Reduction (RRR) is the percent reduction in
risk in the treated group (Y) compared to the control group (X). RRR = 1-RR
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Finding articles of systematic reviews
- Select PubMed@Mercer and
click on Clinical Queries, perform a search, then choose Systematic
- Select PubMed@Mercer,
select Customize under Article types, then select Systematic
Reviews. Enter your search term/s.
Library, enter your search term/s. Select Cochrane Reviews or
- JAMA 1994 272:1367-1371
- ACP Journal Club 1996 May-June; A12-A13
From: Guyatt, G. Users' Guides to the Medical Literature: Essentials of
Evidence-based Clinical Practice. AMA Press, 2002 and Straus. Evidence-Based
Medicine. How to Practice and Teach EBM. Churchill-Livingstone, 3rd
edition, 2005 (pocket cards).
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