Researchers may not have checked all the outcomes (things that can happen) that matter to you in treatment comparisons, and the ones they have checked may not matter to you.
For example, they might only have checked what happened a short time after the treatment, but what happens after a longer time may matter more to you. Or, researchers might have used an outcome that is easy to measure – like a change in a blood test – rather than an outcome that matters to you – like feeling sick.
When researchers use a less important outcome as a substitute for a more important outcome, we cannot be sure that the effect on the important outcome will be the same as the effect on the “substitute outcome”.
REMEMBER: Ask whether the outcomes that are important to you have been checked in fair comparisons of treatments, and look out for substitute outcomes.