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Prev Sci (2013) 14:134143 DOI 10.1007/s11121-013-0377-7
Meta-Analysis and Subgroups
Michael Borenstein & Julian P. T. Higgins
Published online: 13 March 2013# Society for Prevention Research 2013
Abstract Subgroup analysis is the process of comparing a treatment effect for two or more variants of an intervention to ask, for example, if an interventions impact is affected by the setting (school versus community), by the delivery agent (outside facilitator versus regular classroom teacher), by the quality of delivery, or if the long-term effect differs from the short-term effect. While large-scale studies often employ subgroup analyses, these analyses cannot generally be performed for small-scale studies, since these typically include a homogeneous population and only one variant of the intervention. This limitation can be bypassed by using meta-analysis. Meta-analysis allows the researcher to compare the treatment effect in different subgroups, even if these subgroups appear in separate studies. We discuss several statistical issues related to this procedure, including the selection of a statistical model and statistical power for the comparison. To illustrate these points, we use the example of a meta-analysis of obesity prevention.
Keywords Meta-analysis . Research synthesis . Systematic review . Subgroups . Subgroup analysis . Fixed-effect . Fixed-effects . Random-effects
Meta-Analysis and Subgroups
When an intervention is known to be equally effective for all members of a population, it is appropriate to report the impact of that intervention for the population as a whole. By contrast, if the impact varies from one segment of the population to anotherfor example, if an intervention reduces the risk of an event by 80 % for younger people but by only 20 % for older peoplethen the analysis must take account of this difference. This is the goal of subgroup analysis.
The term subgroups can refer to groupings based on a characteristic of the subjects. As above, we may ask if the treatment is more effective for younger persons than for older ones. Subgroups may also be defined by a variant of the intervention. For example, we may ask if an intervention is more effective when delivered by an outside facilitator rather than a regular classroom teacher. Or, subgroups may be defined by elements of the outcome. For example, we may ask if the long-term effect is different than the...