Systematic reviews of diagnostic test evaluations: what’s behind the scenes?

As readers of Evidence-Based Medicine, you are aware that systematic reviews are considered the best source of evidence for evidence-based clinical practice. Systematic reviews synthesise data from existing primary research and bring some order and sanity to the otherwise stressful process of sorting out a plethora of studies and staying up to date. However, since not all reviews are created equal, it is important to be able to critically assess their quality. In this editorial, we take you behind the scenes of a systematic review, using diagnostic test accuracy as an illustration. A clear understanding of the process will, hopefully, guide what you look for in a review. Furthermore, if you can’t find an existing diagnostic review and decide to do one yourself, we provide you with a “road map” (figure) for navigation. Se  =  sensitivity; Sp  =  specificity; LR  =  likelihood ratios; DOR  =  diagnostic odds ratios; ROC  =  receiver operating characteristic; SROC  =  summary receiver operating characteristic; TP  =  true positives; FP  =  false positives; TN  =  true negatives; FN  =  false negatives; TPR  =  true positive rate; FPR  =  false positive rate. Superscripts indicate reference numbers. Systematic reviews are done on a range of clinical questions, such as therapy, diagnosis, prognosis, aetiology, harm, and disease prevalence. All systematic reviews follow the same critical steps: 1. Formulation of the review question 2. A comprehensive, systematic search and selection of primary studies 3. Critical appraisal of included studies for quality and data extraction 4. Synthesis and summary of study results 5. Interpretation of the results These steps resemble those of the evidence-based medicine (EBM) process, but are more thorough. In the EBM process, our objective is to quickly hunt down a valid source …