What is indirectness in a review of studies?
Indirectness refers to the extent to which the populations, interventions, comparisons and outcome measures are dissimilar to those defined in the inclusion criteria for the reviews. Indirectness is important when these differences are expected to contribute to a difference in effect size, or may affect the balance of harms and benefits considered for an intervention. As for the risk of bias, each outcome had its indirectness assessed within each study first. For each study, if there were no sources of indirectness, indirectness was given a rating of 0. If there was indirectness in just 1 source (for example in terms of population), indirectness was given a serious rating of 1, but if there was indirectness in 2 or more sources (for example, in terms of population and treatment) the indirectness was given a very serious rating of 2. A weighted average score was then calculated across all studies contributing to the outcome by taking into account study precision.