Misleading description

Relative effects

Look out for treatment effects that are described as relative effects.

Relative effects (ratios) alone don’t provide enough information for judging the importance of the difference between the two groups. They also may give the impression that a difference is more important than it actually is.

For example, if a treatment cuts the likelihood of getting an illness in half and the baseline risk of a person getting the illness is 2 in 100, receiving the treatment may be worthwhile, even if it also has harmful side-effects. If, however, the risk of getting the illness is 2 in 10,000, then receiving the treatment may not be worthwhile even though the relative effect is the same. The absolute effect of a treatment (the difference) is likely to vary for people at different baseline risk.

REMEMBER: Don’t be tricked by relative effects. Always consider the absolute effects of treatments.