Psychometric Properties of the Neuropsychiatric Inventory: A Review

Abstract

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.

Fig. 1

The skip-question and scoring procedure of the Neuropsychiatric Inventory. This procedure is repeated until all domains are covered.

Fig. 2

Two levels of factor analyses of the Neuropsychiatric Inventory. 1) The syndrome level is where the majority of the NPI factor analytic studies has taken place. The aim of this research is to explore whether latent variables (syndrome ABC), often called a syndrome, would underlie the correlations between different domain scores (A, B, C) of the NPI. These studies implicitly assume that the domain scores can be used as useful indicators for a latent variable. This is the level of factor analytic research reviewed by Canevelli et al. [48]. 2) The subquestion level is critical for establishing structural validity, but it has not been extensively studied, indicated by the dashed lines. The aim of this research is to show that the subquestions (e.g.., A₁, A₂,  ...   A_n) address a unidimensional construct (the one suggested by the screening question), justifying their use in scoring the domain. Structural validity studies can reveal, for example, that the relationships between subquestions and the latent construct are not strong enough, that the subquestions under a single domain address more than one construct like in the study by Gallo et al., or that subquestions from a domain could reflect some other construct instead, or in addition to, the one it is intended to. To explore potential cross-loadings (e.g., C₁ to domain C and A), asking all subquestions from the informant without screening questions is required.