Psychometrics of Assessment: Understanding What Neuropsychology Adds to the Physician’s Understanding of the Patient

Abstract

What is neuropsychology, and what can the physician gain from a neuropsychological study?

To briefly review, neuropsychology is a scientific subspecialty of clinical psychology focused on the study of brain-behavior relationships. Neuropsychologists are subspecialists who hold a doctoral degree in psychology and have also undergone specialized training in the clinical neurosciences. They incorporate knowledge from functional neuroanatomy, neuropathology, behavioral neurology, psychometrics, psychology, and psychiatry to assess and treat the neurocognitive, behavioral, and affective correlates of known or suspected neurological dysfunction. Evaluations provide crucial information for guiding patient care, with the types of questions answerable by a neuropsychologist generally falling into one of six categories (see Lezak et al. Neuropsychological Assessment. Oxford University Press, New York, 2004, for a more expansive review):

The underlying rationale and mechanics of a neuropsychological study

The practice of neuropsychology is not limited to the work of a clinical neuropsychologist. Indeed, physicians frequently assess aspects of cognitive status as a routine component of patient care. For instance, the completion of a neurological exam with basic mental status exam involves screening several neuropsychological functions. However, neuropsychological evaluations performed by a clinical neuropsychologist involve an in-depth, psychometrically based assessment that measures cognitive domains in more depth and breadth than is done in a routine mental status or neurological exam. An important component of this formal assessment process involves establishment of comparative standards for nomothetic and idiographic deficit measurements. In other words, a patient’s performances on various tasks must be compared against benchmarks to allow the neuropsychologist to interpret whether deficits or strengths exist in relation to normative comparison standards (i.e., how the patient performs compared to others), as well as to individual comparison standards (i.e., how the patient’s current performance compares to his/her own premorbid level of baseline functioning). The use of comparison standards is not unique to neuropsychology as species- and population-based comparison standards are used in a variety of laboratory and clinical tests throughout medicine. However, nuances in the application of these approaches to the measurement of neuropsychological deficits do carry some special considerations, which are discussed below.