Level of difficulty for the 20 forms of the Number Facility (NF) and Speed of Closure (SC) subtests of the Repetitive Psychometric Measures was obtained for three samples of Ss. rhos for the level of difficulty of subtests between samples were significant, indicating that level of difficulty is relatively consistent within our samples. Correction factors to adjust for form difficulty were calculated on the basis of one sample; when these adjustment factors were applied to the raw data of a new sample the variability of the form mean around the grand mean was reduced for both subtests, but especially for the SC.
