A direct comparison is a head-to-head comparison of treatments within a study. If there are no direct comparisons of the treatments of interest, indirect comparisons may be possible. The certainty of the evidence for indirect comparisons is lower than for direct comparisons.
For example, consider a comparison of two drugs, A and B. Although studies comparing A and B may be unavailable, studies may have compared A to placebo and B to placebo. This makes it possible to indirectly compare the effect of A and B.
If you feel that this definition hasn't helped you to understand the term, click on our monkey to let us know.