Relative measures of effects can be misleading

This is the twenty-fifth blog in a series of 36 blogs explaining 36 key concepts we need to be able to understand to think critically about treatment claims.

Relative effects (e.g. the ratio of the probability of an outcome in one treatment group compared with that in a comparison group) are insufficient for judging the importance of the difference (between the frequencies of the outcome). A relative effect may give the impression that a difference is larger than it actually is when the likelihood of the outcome
is small to begin with.