![]() ![]() Such studies also allow exposures to be studied that are not obviously ‘interventions’, such as nutritional choices, and other behaviours that may affect health. an over-the-counter preparation or a health education session). These include interventions that a study participant chooses to take (e.g. Including NRSI in a Cochrane Review allows, in principle, the inclusion of non-randomized studies in which the use of an intervention occurs in the course of usual health care or daily life. A mapping of features to some commonly used study design labels can be found in Reeves and colleagues (Reeves et al 2017). We prefer to characterize NRSI with respect to specific study design features (see Section 24.2.2 and Box 24.2.a) rather than study design labels. We also consider controlled trials that use inappropriate strategies of allocating interventions (sometimes called quasi-randomized studies), and specific types of analysis of non-randomized data, such as instrumental variable analysis and regression discontinuity analysis, to be NRSI. Common labels attached to them include cohort studies, case-control studies, controlled before-and-after studies and interrupted-time-series studies (see Section 24.5.1 for a discussion of why these labels are not always clear and can be problematic). NRSI are used by researchers to evaluate numerous types of interventions, ranging from drugs and hospital procedures, through diverse community health interventions, to health systems implemented at a national level. ![]() ![]() ![]() Some of this evidence, especially about harms of interventions, will often need to come from NRSI. (The term observational is used in various ways and, therefore, we discourage its use with respect to NRSI studies see Box 24.2.a and Section 24.2.1.3.) Review authors have a duty to patients, practitioners and policy makers to do their best to provide these groups with a summary of available evidence balancing harms against benefits, albeit qualified with a certainty assessment. Such studies include those in which allocation occurs in the course of usual treatment decisions or according to peoples’ choices (i.e. NRSI are defined here as any quantitative study estimating the effectiveness of an intervention (harm or benefit) that does not use randomization to allocate units (individuals or clusters of individuals) to intervention groups. This chapter aims to support review authors who are considering including non-randomized studies of interventions (NRSI) in a Cochrane Review. Cochrane Handbook for Systematic Reviews of Interventions version 6.3 (updated February 2022). In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Chapter 24: Including non-randomized studies on intervention effects. This chapter should be cited as: Reeves BC, Deeks JJ, Higgins JPT, Shea B, Tugwell P, Wells GA. Review authors should consider how potential confounders, and how the likelihood of increased heterogeneity resulting from residual confounding and from other biases that vary across studies, are addressed in meta-analyses of non-randomized studies. which parts of the study were prospectively designed) rather than ‘labels’ for study designs (such as case-control versus cohort). We recommend that eligibility criteria, data collection and assessment of included studies place an emphasis on specific features of study design (e.g. Non-randomized studies of interventions vary in their ability to estimate a causal effect key design features of studies can distinguish ‘strong’ from ‘weak’ studies.īiases affecting non-randomized studies of interventions vary depending on the features of the studies. Potential biases are likely to be greater for non-randomized studies compared with randomized trials when evaluating the effects of interventions, so results should always be interpreted with caution when they are included in reviews and meta-analyses. For some Cochrane Reviews, the question of interest cannot be answered by randomized trials, and review authors may be justified in including non-randomized studies. ![]()
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