A nephrology guide to reading and using systematic reviews of observational studies

Systematic reviews are an ideal way of summarizing evidence from primary studies. While systematic reviews of randomized trials are broadly used to summarize benefits and harms of interventions, systematic reviews of observational studies are useful to summarize data on prevalence of risk factors in a population, distribution of outcomes or associations of different risk factors with outcomes. Also, systematic reviews can be useful to clarify potential reasons for conflicting data found in primary studies and explore sources of heterogeneity (variation in primary study data) to better understand epidemiological data and generate hypotheses for candidate interventions to improve outcomes. Summarizing data from observational studies in systematic reviews is a powerful tool to distil existing prognostic evidence in specific settings and inform patients and healthcare providers. In this article, we describe how to critically appraise the methods, interpret the results and apply the findings of a systematic review of observational (prognostic) studies.