Look out for results that are reported for a selected group of people within a study or systematic review.
Comparisons of interventions often report results for selected groups of participants, called “subgroups”. This is because people want to know whether the effect of an intervention is different for different types of people (e.g. men and women or different age groups).
But subgroup analyses are often poorly planned and reported. Most differential effects suggested by these “subgroup results” are likely to be due to the play of chance and are unlikely to reflect true differences in the effect of an intervention between different subgroups of people.
REMEMBER: Treatment effects that are based on the results for subgroups of people may be misleading.