2-17 Don’t confuse “no evidence” with “no effect”

Systematic reviews sometimes conclude that there is “no evidence” of effect when there is uncertainty about the difference between two treatments. This is often misinterpreted as meaning that there is no difference between the treatments compared. However, studies can never show that there is “no effect” or “no difference”. They can only rule out important effects or differences.

Don’t be misled by statements of “no effect” or ”no difference” between treatments. Consider instead the degree to which it is possible to confidently rule out an important difference.