Even so, for the reasons already outlined, the methods exployed by experimental psychology are incapable of accommodating differential variables and the methods of correlational psychology are incapable of revealing the critical features of individual processes. Many have hinted that efforts to resolve the conflict between experimentalists and correlationists have been hampered by the lack of an appropriate methodology for embedding individual performance within a model of individual differences, one that will support predictions of behavior of the organism under specified situations.
Suggestions are aplenty.
No such method has been presented but encouraging signposts on the road to an integrated model have appeared. In 1945, Clark Hull boldly suggested that a natural-science approach to behavior theory must bridge the concerns of traditional academic psychology with the efforts of differential psychology. He proposed that this may be accomplished by estimating natual laws with individualized empirical constants. The variation in the empirical constants accounts for individual differences in behavior. However, Hull's attempts to demonstrate his approach were inconclusive but he continued to voice the need for an appropriate addition to experimental methodology which would deal with individual differences.