Metrics
Effective frequency
Effective frequency is the number of exposures a person needs before an ad achieves its communication goal - awareness, recall or action. Planning to effective frequency means buying enough repetition to register without paying for exposures past the point of usefulness.
In practice
The classic heuristic of three-plus exposures is a starting point, not a law; the real number moves with message complexity, brand familiarity and category attention levels.
Effective frequency turns reach planning into reach-at-weight planning: the target becomes '60% of the audience at 3+' rather than reach alone.