OBJECTIVES: Previous factor analytic studies of the WAIS, WAIS-R and WAIS-III used standardization samples, (representing the general population), clinical populations (e.g. psychiatric) and 'non-clinical' groups (e.g. older adults). These studies endorsed the reliability of the scales in such samples and supported theoretical models of intelligence. The WAIS-III (1997) includes four Indexes based on factor analysis, which provide clinically useful information to practitioners, but have not been validated in a low IQ population. However, the WAIS-III is often administered to individuals with suspected or proven low IQ, as it offers service providers, legislators and the Department of Health with a reliable measure of IQ. The aim of this study was to investigate the factor structure of the WAIS-III in a low IQ sample. METHODS: WAIS-III data was collected from assessments carried out in routine clinical practice from individuals with a full scale IQ of 74 or below (n=105). The data were subjected to factor analysis, using two types of factor analysis: principal axis factoring and principal components analysis. Orthogonal and oblique rotations were applied to the analyses. RESULTS: Only one robust solution could be extracted. This contained two factors, analogous to traditional verbal and performance sub-scales. CONCLUSIONS: This study does not support the four-factor solution which underlies WAIS-III index scores in a low IQ population.
OBJECTIVES: Previous factor analytic studies of the WAIS, WAIS-R and WAIS-III used standardization samples, (representing the general population), clinical populations (e.g. psychiatric) and 'non-clinical' groups (e.g. older adults). These studies endorsed the reliability of the scales in such samples and supported theoretical models of intelligence. The WAIS-III (1997) includes four Indexes based on factor analysis, which provide clinically useful information to practitioners, but have not been validated in a low IQ population. However, the WAIS-III is often administered to individuals with suspected or proven low IQ, as it offers service providers, legislators and the Department of Health with a reliable measure of IQ. The aim of this study was to investigate the factor structure of the WAIS-III in a low IQ sample. METHODS: WAIS-III data was collected from assessments carried out in routine clinical practice from individuals with a full scale IQ of 74 or below (n=105). The data were subjected to factor analysis, using two types of factor analysis: principal axis factoring and principal components analysis. Orthogonal and oblique rotations were applied to the analyses. RESULTS: Only one robust solution could be extracted. This contained two factors, analogous to traditional verbal and performance sub-scales. CONCLUSIONS: This study does not support the four-factor solution which underlies WAIS-III index scores in a low IQ population.