NHP or SIP--a comparative study in renal insufficiency associated anemia

Abstract

In this study we compared the feasibility, internal structure and psychometric characteristics (internal consistency, test-retest reliability, construct validity) of two widely used generic health status measures, i.e. the Nottingham Health Profile (NHP) and the Sickness Impact Profile (SIP) when employed among a sample of patients on renal dialysis (n = 63). The NHP was found to be more feasible, i.e. shorter and less difficult, than the SIP. The NHP scales showed somewhat higher levels of internal consistency (mean alpha = 0.67, range = 0.39-0.80) than the SIP scales (mean alpha = 0.65, range = 0.14-0.82). Test-retest reliability with a 24-hour interval was acceptable for most NHP scales (not available for the SIP in this study). Intercorrelations between the NHP scales were somewhat weaker than those for the SIP, and the expected patterns of scale intercorrelations were largely confirmed. The overall pattern of correlations between NHP scales and SIP scales was consistent with expectations, although the correlations were generally rather weak. Correlations between NHP scales and SIP scales and instruments measuring mainly physical functioning (ADL, Karnofsky) were largely as expected. Similarly, correlations between NHP scales and SIP scales and instruments measuring mainly psychological functioning [STAI (anxiety), SDS-Zung (depression)] were also as expected, although here the correlations were weaker for the SIP when compared with the NHP. The Index of Well-being exhibited intra-class correlations > 0.3 with one SIP scale and with five out of six NHP scales. Common factor analysis, yielding a two-factor solution with a physical and a mental factor of equal importance, showed the SIP scales to load more on the physical factor, while the NHP scales loaded more on the mental factor. The NHP generally performed better than the SIP in terms of feasibility and internal consistency. Physical functioning is emphasized in the SIP, whereas the emphasis of the NHP lies on mental functioning. The analysis confirmed to some extent the intentions of the constructors of NHP and SIP respectively, i.e. the NHP to be a measure of perceived health and the SIP to be a more functional measure.