Chapter 8 – Effect Measures – Systematic Reviews in Health Research

Julian P.T. Higgins, Jonathan J. Deeks, Douglas G. Altman

Abstract

Here we describe the different effect measures that are typically used in meta-analyses of randomized trials, many of which are also used in observational studies. For dichotomous data (e.g. dead or alive), the three main options are the odds ratio (OR), the risk ratio (RR) and the risk difference (RD). We describe how these are computed from results of individual trials, along with measures of uncertainty. For continuous outcomes (e.g. body mass index), the three main options are the difference in means, a standardized difference in means, and the ratio of means (RoM). Again, we provide computational formulae for these, and we also discuss effect measures suitable for time-to-event outcomes, rates, and ordinal outcomes. We then explore how one might decide among different effect measures when several are available. The key considerations are (i) the likelihood that effects will be consistent across studies, (ii) mathematical properties, and (iii) ease of interpretation. We close with two case studies to illustrate some of these ideas.

Corrections

Figure 8.3, heading (b) should read “Heterogeneity: RR compared to RD“

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Author affiliations

Julian P.T. Higgins

Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK
National Institute of Health Research, Applied Research Collaboration West, University Hospital Bristol and Weston NHS Foundation Trust, Bristol, UK

Jonathan G. Deeks

Test Evaluation Research Group, Institute of Applied Health Research, University of Birmingham, Birmingham, UK

Douglas G. Altman

Centre for Statistics in Medicine, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, UK

How to cite this chapter?

For the printed version of the book

Higgins, J.P.T., Deeks, J.J. and Altman, D.G. (2022). Chapter 8. Effect measures. In: Systematic Reviews in Health Research: Meta-analysis in Context (eds M. Egger, J.P.T. Higgins and G. Davey Smith), pp 129-158. Hoboken, NJ : Wiley.