The lack of research evidence of a beneficial or negative effect of an intervention is not the same as evidence of “no difference”. Evidence of an intervention not being effective (or harmful) is different to there not yet being sufficient research evidence to conclude whether something is effective (or harmful).
Systematic reviews and other studies sometimes conclude that there is “no evidence of a difference” when there is uncertainty about the difference between two interventions. This is often misinterpreted as meaning that “there is no difference” between the interventions compared. However, studies can never show that there is “no difference” (“no effect”). They can only rule out, with specific degrees of confidence, differences of a specific size.
BEWARE of statements that claim “no difference” between interventions (“no effect”).
REMEMBER to consider instead the degree to which it is possible to confidently rule out a difference of a specified size.