nck's early research in the psychology of aesthetics, hypnosis, and projective tests led him to become "dismissive of psychoanalytic thinking" and after the War he allied himself with the general behaviorist trend developed by B. F. Skinner (Brand 67). Eysenck insisted on the use of experimental evidence, "even if such evidence had to come chiefly from animals" (Brand 67). Among his extensive work with testing were various experiments in the area of intelligence assessment where he applied factor analysis in furthering the development of the hierarchical model of intelligence in which, as he confirmed, primary factors (such as numerical ability or word fluency) "are correlated together to form a general factor of intelligence"--an idea that is now widely accepted among factor analysts (Wilson 426).
Eysenck also developed a more detailed approach to the analysis of IQ scores and demonstrated that three factors, speed of functioning, accuracy and persistence, can vary independently. The understanding of standard IQ scores as a coalescence of these factors was a significant improvement in their usefulness. Eysenck believed that further experimental work on the "relative heritability and modifiability" of these factors might demonstrate whether they were more or less susceptible to the influences of learning and motivation (Wi
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