Look out for results that are reported for a selected group of people within a study or systematic review.
Comparisons of treatments often report results for selected groups of participants, called “subgroups”. This is because people want to know whether the effect of a treatment 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 a treatment between different subgroups of people.