Incremental Validity of the Quick Test
The purpose of the present study was to determine whether the Quick Test (QT) of intelligence (Ammons & Ammons, 1962) has incremental validicy in a private psychiatric setting. The construct and concurrent validity of the QT have already been demonstrated (e.g., Davis & Dizzone, 1970). However, as has already been pointed out (Cronbach & Gleser, 1965; Meehl & Rosen, 1955; Sechrest, 1963), in order for a test to be useful it must also possess greater validity than the a priori state of knowledge allows. Sechrest termed this practical requirement "incremental validity." With regard to the clinical use of a brief intelligence test, it means that the device ought to have greater accuracy than the clinical impression of the person making the referral. Ss were 31 heterogeneous psychiatric patients at the Carrier Clinic, a private psychiatric hospital. They ranged from 17 to 64 yr., with a mean age of 32.51 yr. Thirteen were male and 18 female. The patients were referred for an intellectual assessment by 10 different psychiatrists who gave their estimate of Full Scale Wechsler Adult Intelligence Scale (WAIS) IQ. Form 1 of the QT was administered. The mean and SD of the WAIS, QT, and psychiatrist-estimated IQs are presented in Table 1. The mean psychiatrists' estimate was 9.03 points higher than the Full Scale WAIS, and this contrasts with the mean QTI IQ being 1.74 points higher ( t = 2.90, p < .01). When the sign of the deviations from WAIS 1Q is not considered, the mean deviations are 8.00 for QT and 11.94 for psychiatric estimates ( t = 2.63, p < .05).