Estimates of premorbid ability in a neurodegenerative disease clinic population: comparing the Test of Premorbid Functioning and the Wide Range Achievement Test, 4th Edition.

Objective: Two frequently used measures to assess premorbid intellectual ability include the Wide Range Achievement Test, 4th Edition Reading Subtest (WRAT-4 READ) and the Test of Premorbid Functioning (TOPF). The present study compared estimates obtained from these measures in a neurodegenerative disease population. Method: Records from 85 referrals seen for neuropsychological evaluation in a neurodegenerative disorders clinic were reviewed. Evaluations included TOPF, WRAT-4 READ, and measures of memory, reasoning, language, and executive functioning. Pairwise correlations and concordance correlation coefficients (CCC) were calculated between raw scores and predicted intelligence estimates. Discrepancy scores were calculated between estimates and data were divided into three groups based on size of standardized discrepancy score: Equal, WRAT-4 READ>TOPF, and TOPF>WRAT-4 READ. analysis of variances compared groups on demographic characteristics and cognitive performance. Results: Despite strong Pearson correlation, CCC between predicted IQ estimates showed poor agreement between measures, with evidence of both fixed and proportional bias. Discrepancies ranged from -24.0 to 22.0 (M=1.78, SD=6.65), with TOPF generating higher estimates on average. Individuals performing better on WRAT-4 READ were significantly older (M age=76.26, SD=7.53) than those performing similarly on both measures and those performing better on TOPF (F (2, 82)=7.31, p<.001). All other comparisons between groups on demographic variables and cognitive measures were non-significant. Conclusions: Estimates of premorbid intelligence obtained from the TOPF and WRAT-4 READ have a strong linear relationship, but systematically generate inconsistent estimates in a neurodegenerative disease clinical sample and should not be used interchangeably.