What is normal cognition in depression? Prevalence and functional correlates of normative versus idiographic cognitive impairment

Objective Traditional neuropsychological assessment methods identify a subpopulation of individuals with Major Depressive Disorder (MDD) who demonstrate cognitive functioning below population norms. An even larger proportion of those with MDD self-report problems with cognition that interfere with daily roles and responsibilities. We aim to test whether an intraindividual deviation of cognitive functioning relative to premorbid estimates (idiographic impairment) may better characterize challenges for functional recovery in MDD. Method Adult participants with MDD (N = 111) who completed a baseline neuropsychological assessment battery for a cognitive remediation trial were used in analyses. We compared the frequency of cognitive impairment using the normative and idiographic approaches and examined how these indexes related to observed functioning, perceived functioning, and depression severity. Results While only 25% of the sample would be classified as cognitively impaired on a composite measure according to normative comparison standards, 62.2% of this group were classified as idiographically impaired using a conservative cut-off of at least 1 SD deviation below premorbid estimates. Idiographic cognitive impairment shared a stronger inverse relationship with perceived functional competence than normative cognitive impairment. Depressive symptoms did not significantly correlate with both normative and idiographic impairment. Conclusions In MDD, reliance on assessment of contemporary cognitive functioning might underestimate rates of those who could be considered cognitively impaired. Consideration of idiographic impairment may help explain gaps between normatively defined cognitive ability with subjective complaints and disability in MDD. (PsycInfo Database Record (c) 2021 APA, all rights reserved).