Demographic corrections appear to compromise classification accuracy for severely skewed cognitive tests

Abstract

Demographic corrections for cognitive tests should improve classification accuracy by reducing age or education biases, but empirical support has been equivocal. Using a simulation procedure, we show that creating moderate or extreme skewness in cognitive tests compromises the classification accuracy of demographic corrections, findings that appear replicated within clinical data for the few neuropsychological test scores with an extreme degree of skew. For most neuropsychological tests, the dementia classification accuracy of raw and demographically corrected scores was equivalent. These findings suggest that the dementia classification accuracy of demographic corrections is robust to slight degrees of skew (i.e., skewness <1.5).

Keywords:

• Classification accuracy
• Dementia
• Skew
• Test properties

Acknowledgments

M. E. O'Connell was aided in the manuscript preparation by a Dr. Janet Bews and Alzheimer Society of Canada/CIHR (Institute of Aging) Doctoral Award. A research personnel award from the Canadian Institutes of Health Research, Institute of Aging provided support for the second author in the preparation of this manuscript as did a Michael Smith Foundation for Health Research award for research unit infrastructure held by the Centre on Aging at the University of Victoria. The Canadian Study of Health and Aging (CSHA) was funded by the Seniors' Independence Research Program, through the National Health Research and Development Program (NHRDP) of Health Canada, Project 6606–3954-MC(S). Additional funding for the CSHA was provided by Pfizer Canada Incorporated through the Medical Research Council/Pharmaceutical Manufacturers Association of Canada Health Activity Program, NHRDP, Project 6603–1417–302 (R), Bayer Incorporated, the British Columbia Health Research Foundation, Projects 38 (93–2) and 34 (96–1). The study was coordinated through the University of Ottawa and the Division of Aging and Seniors, Health Canada.