Cognitive function index for patients with chronic fatigue syndrome

Background: A comprehensive approach to assessing neuropsychological deficits in CFS patients is developed by assessing cognitive function across a number of domains using a battery of tests, rather than relying on any single instrument. Objective: A factor analytic approach was employed to examine the underlying dimensionality of 15 standard cognitive function related test variables in CFS patients. A cognitive function index (CFI) was then developed using appropriately weighted and interpreted factors. Methods: Factor analysis was applied to an initial sample of 65 CFS patients, identifying eight factors accounting for over 70% of total variation. This factor structure was then independently verified on a separate sample of 124 CFS patients. An overall combined CFS sample of 212 was then used to derive the CFI using an appropriately interpreted and weighted average of the derived factors. Results: After including age and education as separate factors, the CFI consists of nine factors accounting for 70% of total variation in the overall CFS group. The CFI was not affected by the presence of current psychiatric comorbidity. A cut-off score for cognitive dysfunction was established using the lower quartile value of a group of sedentary controls on the same index. Conclusions: The CFI will provide a useful summary measure for researchers investigating cognitive function performance in CFS patients. It does not replace existing individual specialized tests.