In this paper, we report on the development of a new state-of-the art instrument to measure NPS in people with dementia and the results from an international validation study. The NPI-C capitalizes on the existing strength of NPI and has rectified the weaknesses of NPI. Overall, the NPI-C is responsive to shortcomings in NPS measures and has the potential to function as a single tool that could be used in clinical trials either as a “broad spectrum” assessment across many domains or for “in-depth” monitoring of a limited set of domains (Lyketsos, 2007
We first note that nested within the NPI-C are the original NPI items. This provided us with the opportunity to examine ICCs and convergent validity using clinician ratings for this widely used measure. Twelve original items had ICC values <0.5, the majority of which (n = 5) were in the domain of hallucinations. One item (item 4) in hallucinations lacked variability; three (items 5–7) had an ICC value of 0.00. This discrepancy may point to conflicting responses by caregivers and/or patients regarding the occurrence of various types of hallucination-related behaviors and/or relative infrequency of them, in which any small discrepancy would affect the ICC value. Other NPI domains with low ICC items were delusions (item 7); elation (item 5), disinhibition (item 4), aberrant motor (items 4 and 6), and sleep disturbances (item 6).
For the NPI-C items that were not part of the original NPI, the domain with highest number of items <0.50 was “aggression.” Five items lacked any variability, suggesting their occurrence may be too rare to be worthwhile. Three new items in “agitation” also had ICC values <0.50. Overall, a total of 17 items were removed (see ). For the remaining items, ICCs were moderate to strong. Although three items were removed in the new domain of aberrant vocalizations (ICC = 0.23), the eight remaining items had values ranging from 0.70 to 0.96. This suggests that the new domain may provide useful and previously unreported information on this behavior, which is relevant for people in moderate to severe dementia stages.
Convergent validity was moderate to strong for the four domains and their corresponding measures. “Apathy” had the weakest correlation (r = 0.31) for the NPI-C. We note that the correlation for the NPI global domain rating was much lower (r = 0.22). One factor possibly contributing to the weaker correlation is the absence of data from the Brazil site. Inconsistencies in the translation of the AES necessitated the exclusion of data from this site (n = 15). Although Camozzato and colleagues (2008)
reported reliability data for the Brazilian Portuguese version of the NPI, they did not examine validity, specifically whether the cultural interpretation of apathy-related items were similar in Brazilian caregivers as in other languages. It is interesting to note that Camozzato et al.
found higher scores of severity and distress in the apathy domain than in any other NPI domain.
The strength of correlation between “agitation” and the CMAI for the NPI-C was moderate (r = 0.40), but increased substantially when the domain of aberrant vocalization was added (r = 0.60). The correlation was very weak, however, for the domain rating of agitation in the NPI (r = 0.19). Although the correlation strengthened for the NPI with the addition of aggression (r = 0.31), it was still not as strong as the NPI-C agitation domain alone and the CMAI. This points to the potential usefulness of the NPI-C agitation domain as a “stand alone” measure in trials. Another domain that shows strength as a stand-alone measure is the depression/dysphoria domain of the NPI-C (r = 0.61), which showed significant improvement over the NPI for the same domain (r = 0.31).
At this stage of the scale development, the NPI-C has not yet been incorporated into any clinical trials and its sensitivity to change is unknown. The raters in the current study were experienced in dementia research and in the assessment of NPS, and came from different clinical and research backgrounds. They included nurses, physicians, gerontologists, social workers and others with research expertise. The performance of the NPI-C in multicenter trials including raters of varying levels of expertise requires further investigation. Due to small samples sizes at each of the site, we are not able to assess reliability across languages and sites at this time but will address this shortcoming in future studies.
Overall, the study results demonstrate the utility of the NPI-C as a measuring tool of NPS in clinical trials. There are several notable advantages to this measurement approach. The NPI-C allows the flexibility of simultaneously administering the NPI. Since original NPI items are included, researchers can record NPI-C data in addition to NPI scores, which will facilitate cross-trial and site comparisons. Several NPI-C domains also show promise as stand-alone measures, which will also facilitate study comparison and eliminate the need to include other outside measures. This can improve uniformity in study design and reduce error and administration time. The availability of the NPI-C in several languages through this validation study is another added benefit.
Overall, the NPI-C is a universal tool that can accurately measure several NPS. It uses a uniform scale system, which will facilitate data comparisons across studies. The NPI-C may be extremely useful in several settings, including clinical trials, observational studies, and potentially in clinical practice as well.