Neuropsychiatric symptoms cause a significant burden to individuals with neurocognitive disorders and their families. Insights into the clinical associations, neurobiology, and treatment of these symptoms depend on informant questionnaires, such as the commonly used Neuropsychiatric Inventory (NPI). As with any scale, the utility of the NPI relies on its psychometric properties, but the NPI faces unique challenges related to its skip-question and scoring formats. In this narrative review, we examined the psychometric properties of the NPI in a framework including properties pertinent to construct validation, and health-related outcome measurement in general. We found that aspects such as test-retest and inter-rater reliability are major strengths of the NPI in addition to its flexible and relatively quick administration. These properties are desired in clinical trials. However, the reported properties appear to cover only some of the generally examined psychometric properties, representing perhaps necessary but insufficient reliability and validity evidence for the NPI. The psychometric data seem to have significant gaps, in part because small sample sizes in the relevant studies have precluded more comprehensive analyses. Regarding construct validity, only one study has examined structural validity with the NPI subquestions. Measurement error was not assessed in the reviewed studies. For future validation, we recommend using data from all subquestions, collecting larger samples, paying specific attention to construct validity and formulating hypotheses a priori. Because the NPI is an outcome measure of interest in clinical trials, examining measurement error could be of practical importance.
Keywords: Alzheimer’s disease; Neuropsychiatric Inventory; behavioral and psychological symptoms of dementia; dementia; measurement; neuropsychiatric symptoms; reliability; validity.