NECESSITY/SUFFICIENCY AS A CONCEPTUAL MODEL FOR PREDICTOR-CRITERION RELATIONSHIPS.

The concepts of necessity and sufficiency are presented as the basis for understanding various predictor-criterion relationships. Three types of strong relationships are introduced as models for the discovery, utilization, and evaluation of predictors 1 necessary-and-sufficient, the conventional symmetrical relationship where the frequencies in two cells of the four-fold table approach zero as the association increases, 2 necessary-but-not-sufficient, the asymmetrical relationship where the frequency in only the false-positive cell approaches zero, and 3 sufficient-but-not-necessary, the asymmetrical relationship where the frequency in only the false-negative cell approaches zero. It is shown that the necessary-and-sufficient model is a poor basis for the discovery, utilization, and validation of necessary-but-not-sufficient and sufficient-but-not-necessary predictors. Due to over-emphasis of the necessary-and-sufficient model, it is likely that many potentially useful predictors have been discarded as useless. An improved methodology is suggested. Author