Summary
The aim of this study was to develop a specific and valid questionnaire for Italian COPD patients, living on the north or the south of Italy—which are two culturally distinct areas.
The project consisted in three steps: (1) initial item set generation to identify items relevant to both genders, all ages and both regions; (2) item reduction including tests of regional specificity; (3) tests of internal validity using item- response theory using Rasch one-parameter modelling.
Ninty-six COPD patients (mean aged 69 yr; 78 Male) completed the original set of 124 items of the Italian Health Status Questionnaire (IHSQ). Item reduction was carried out using an established standardised approach employing classical psychometric test theory. The internal construct validity of the 47 items that survived this process were tested to determine whether they constituted a unidimensional construct ‘‘impaired health due to COPD’’ using Rasch analysis. This showed that the questionnaire had very good psychometric properties, with an excellent Person Separation Index of 0.95 and no evidence of bias due to item–trait interaction (w2104 1⁄4 127:1, P 1⁄4 n:s:).

Relevance
this study combine a structured application of classical test theory as described by O’Leary and Jones,1 with the Rasch modelling to develop a disease-specific questionnaire to mea- sure health status in Italian patients with COPD.