2-3 Peoples’ outcomes should be analyzed in their original groups

Randomized allocation helps to ensure that the groups have similar characteristics. However, people sometimes do not receive or take the allocated treatments. The characteristics of such people often differ from those who do take the treatment as allocated. Therefore, excluding from the analysis people who did not receive the allocated treatment may mean that like is no longer being compared with like.

Be cautious about relying on the results of treatment comparisons if patients’ outcomes are not counted in the group to which they were allocated. For example, in a comparison of surgery and drug treatments, people who die while waiting for surgery should be counted in the surgery group, even though they did not receive surgery.