rule of threerule of three
- (mathematics education) A rule stating that, if two ratios are equal, then the denominator of the second equals its numerator times the reciprocal of the first ratio: if then .
- (medicine) A rule for clinical trials used for determining the rate of adverse side effects when no such side effects present during the course of the trial.
- (writing, rhetoric) A rule which states that things which come in groups of three are inherently funnier or more effective than things which come in groups of other sizes.
- (religion, Wicca) A religious tenet stating that whatever energy a person puts out into the world, be it positive or negative, will be returned to that person three times.