Biomaterial Database

Systematic reviews: how they work and how to use them. 2007

J B Carlisle

Department of Anaesthetics, Torbay Hospital, Lawes Bridge, Torquay, Devon TQ2 7AA, UK. john.carlisle@nhs.net

At their best, systematic reviews should be the least biased summaries of the effect of healthcare interventions. However, authors can introduce both intended and unintended biases into systematic reviews. Results presented as odds ratios are often misinterpreted by readers as relative risks, meaning that the effect of the intervention is overestimated. Authors may analyse trials separately having mistaken differences in baseline risk for differences in the effect of an intervention and differences in effect between trials that have been analysed together may go undetected. In this article I discuss how a systematic review should work and how it can go wrong.

UI	MeSH Term	Description	Entries
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D012196	Review Literature as Topic	Works about published materials which provide an examination of recent or current literature. These articles can cover a wide range of subject matter at various levels of completeness and comprehensiveness based on analyses of literature that may include research findings. The review may reflect the state of the art and may also include reviews as a literary form.	State-of-the-Art Review,State-of-the-Art Reviews,Review, State-of-the-Art,Reviews, State-of-the-Art,State of the Art Review,State of the Art Reviews
D012680	Sensitivity and Specificity	Binary classification measures to assess test results. Sensitivity or recall rate is the proportion of true positives. Specificity is the probability of correctly determining the absence of a condition. (From Last, Dictionary of Epidemiology, 2d ed)	Specificity,Sensitivity,Specificity and Sensitivity
D015982	Bias	Any deviation of results or inferences from the truth, or processes leading to such deviation. Bias can result from several sources: one-sided or systematic variations in measurement from the true value (systematic error); flaws in study design; deviation of inferences, interpretations, or analyses based on flawed data or data collection; etc. There is no sense of prejudice or subjectivity implied in the assessment of bias under these conditions.	Aggregation Bias,Bias, Aggregation,Bias, Ecological,Bias, Statistical,Bias, Systematic,Ecological Bias,Outcome Measurement Errors,Statistical Bias,Systematic Bias,Bias, Epidemiologic,Biases,Biases, Ecological,Biases, Statistical,Ecological Biases,Ecological Fallacies,Ecological Fallacy,Epidemiologic Biases,Experimental Bias,Fallacies, Ecological,Fallacy, Ecological,Scientific Bias,Statistical Biases,Truncation Bias,Truncation Biases,Bias, Experimental,Bias, Scientific,Bias, Truncation,Biase, Epidemiologic,Biases, Epidemiologic,Biases, Truncation,Epidemiologic Biase,Error, Outcome Measurement,Errors, Outcome Measurement,Outcome Measurement Error
D016017	Odds Ratio	The ratio of two odds. The exposure-odds ratio for case control data is the ratio of the odds in favor of exposure among cases to the odds in favor of exposure among noncases. The disease-odds ratio for a cohort or cross section is the ratio of the odds in favor of disease among the exposed to the odds in favor of disease among the unexposed. The prevalence-odds ratio refers to an odds ratio derived cross-sectionally from studies of prevalent cases.	Cross-Product Ratio,Risk Ratio,Relative Odds,Cross Product Ratio,Cross-Product Ratios,Odds Ratios,Odds, Relative,Ratio, Cross-Product,Ratio, Risk,Ratios, Cross-Product,Ratios, Risk,Risk Ratios
D016032	Randomized Controlled Trials as Topic	Works about clinical trials that involve at least one test treatment and one control treatment, concurrent enrollment and follow-up of the test- and control-treated groups, and in which the treatments to be administered are selected by a random process, such as the use of a random-numbers table.	Clinical Trials, Randomized,Controlled Clinical Trials, Randomized,Trials, Randomized Clinical