An analysis of random and systematic changes with practice

Six motor tests and six nonverbal tests were administered four times to the same subjects. Subjective reports of the subjects are discussed, changes in mean scores and in variability and score correlations from trial to trial are surveyed, and factor analyses of results on the first and fourth trials are presented and compared. Implications of the findings with respect to correction for attenuation are pointed out.Thanks are due to Mr. Searles and his staff at the Henry Ford Trade School, who gave both suggestions and aid in completing this work; to Dr. L. L. Thurstone, who gave suggestions for certain aspects of the analysis; and to L. R. Tucker and Robert Blakey, who made the final factorial analyses and suggested various conclusions.