Impairment versus deficiency in neuropsychological assessment: Implications for ecological validity

Neuropsychological test interpretation has relied on pre- and postmorbid comparisons, as exemplified by the use of demographically adjusted normative data. We argue that, when the assessment goal is to predict real-world functioning, this interpretive method should be supplemented by "absolute" scores. Such scores are derived from comparisons with the general healthy adult population (i.e., demographically unadjusted normative data) and reflect examinees' current ability, that is, the interaction between premorbid and injury/disease-related factors. In support of this view, we found that substantial discrepancies between demographically adjusted and absolute scores were common in a traumatic brain injury sample, especially in participants with certain demographic profiles. Absolute scores predicted selected measures of functional outcome better than demographically adjusted scores and also classified participants' functional status more accurately, to the extent that these scores diverged. In conclusion, the ecological validity of neuropsychological tests may be improved by the consideration of absolute scores. (JINS, 2009, 15, 94-102.).