Assessing the robustness of the Test of Premorbid Functioning (TOPF) as a measure of premorbid intelligence in Alzheimer’s and vascular dementia and clinical research portfolio

McDonald, Alexa (2015) Assessing the robustness of the Test of Premorbid Functioning (TOPF) as a measure of premorbid intelligence in Alzheimer’s and vascular dementia and clinical research portfolio. D Clin Psy thesis, University of Glasgow.

Abstract

Introduction: The Test of Premorbid Functioning (TOPF) is a relatively new reading test designed to estimate premorbid intelligence in people with a diagnosed or suspected dementia. A discrepancy between premorbid and current functioning is indicative of cognitive decline. Previous studies have reported mixed results on the validity of reading tests in people with dementia, and the TOPF has yet to be investigated as to how well it holds in dementia.

Objectives: To assess the robustness of the TOPF against the Spot-the-Word (version 2; STW-2) and a demographic regression equation in estimating premorbid ability in people with Alzheimer’s disease (AD), vascular dementia (VD) and mixed dementias (AVD).

Design: A cross-sectional study with two groups of participants assessed on three measures of premorbid ability.

Methods: Thirty patients with an ICD-10 diagnosis of probable AD, VD or ADV were recruited from two NHS Older Adult Community Mental Health teams and their scores on the TOPF, STW-2 and a demographic equation were compared with thirty healthy matched controls.

Results: Significant between-group differences were found for both the TOPF and STW-2, with an average difference of 5-7 IQ points and a medium effect size. The results suggest that both reading tests systematically under-estimated premorbid IQ in the dementia group. The demographic equation provided a significantly higher estimation of IQ than both of the reading tests for people with a dementia. When the dementia group was arbitrarily split into a “less impaired” and “more impaired” group, based on the median ACE-III score of 65, there was still a medium effect size between the healthy controls and the dementia groups on the TOPF and STW-2.

Conclusion: The findings of this study suggest that the TOPF underestimates premorbid IQ in people with a dementia. Clinicians should exercise caution when interpreting the results of reading tests by considering and reporting the confidence intervals for obtained-minus-predicted IQ discrepancies and with clear reference to the clinical history and other cognitive test results. These findings are discussed with respect to the literature on the validity of reading tests and recommendations for future research are provided. Limitations of the study included a modest sample size and the use of a demographic equation which has not been normed against the current WAIS-IV.

Practitioner points:
1) The TOPF and STW-2 provide similar estimates of premorbid IQ in people with a dementia.
2) Both reading tests systematically underestimated premorbid ability in people with a dementia, by between 5 and 7 IQ points.
3) When using reading tests to determine an obtained-minus-predicted discrepancy score, confidence intervals should be considered and reported in the analysis and there should be clear reference to the clinical history and other cognitive test results.
4) This study was based on a modest sample size and utilised a demographic equation which has not been normed against the current WAIS-IV.

• Item Type: Thesis (D Clin Psy)
• Qualification Level: Doctoral
• Keywords: dementia; premorbid intelligence
• Subjects: B Philosophy. Psychology. Religion > BF Psychology
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Health & Wellbeing > Mental Health and Wellbeing
• Supervisor's Name: Evans, Professor Jonathan
• Date of Award: 2015
• Depositing User: Mrs Alexa McDonald
• Unique ID: glathesis:2015-6793
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 29 Dec 2015 09:47
• Last Modified: 29 Dec 2015 10:03
• URI: https://theses.gla.ac.uk/id/eprint/6793