Key points
- •
Quality of evidence (our confidence in estimates of effect) may decrease when substantial differences exist between the population, the intervention, or the outcomes measured in relevant research studies and those under consideration in a guideline or systematic review.
- •
Quality of evidence decreases if head-to-head comparisons are unavailable. Such instances require falling back on indirect comparisons in which, for example, we make inferences about the relative effect of two interventions on the basis of their comparison not with one another, but with a third or control condition.