Rasch measurement for reducing the items of the Nottingham Health Profile

The present study aimed to develop a short form of the Spanish version of the Nottingham Health Profile (NHP) by means of Rasch analysis. Data from several Spanish studies that included the NHP since 1987 were collected in a common database. Forty-five different studies were included, covering a total of 9,419 subjects both from the general population and with different clinical pathologies. The overall questionnaire (38 items) was simultaneously analyzed using the dichotomous response model. Parameter estimates, model-data fit and separation statistics were computed. The items of the NHP were additionally regrouped into two different scales: Physical (19 items) and Psychological (19 items). Separated Physical and Psychological parameter estimates were produced using the simultaneous item calibrations as anchor values. Misfitting items were deleted, resulting in a 22 item final short form (NHP22)-11 Physical and 11 Psychological-. The evaluation of the item hierarchies confirmed the construct validity of the new questionnaire. To demonstrate the invariance of the NHP22 item calibrations, Rasch analyses were performed separately for each study included in the sample and for several sociodemographic and health status variables. Results confirmed the validity of using the NHP22 item calibrations to measure different groups of people categorized by gender, clinical and health status.