TABLE 2

Summary of Rasch analysis

Rasch statisticsBHQ total score
Number of items10
Chi-squared fit statistic28.16
Degrees of freedom20
p-value0.11
Item fit residual (mean±sd)0.01±1.11
Person fit residual (mean±sd)−0.25±1.11
PSI0.85
Cronbach's α0.85
  • BHQ: Bronchiectasis Health Questionnaire; PSI: Person Separation Index. The Chi-squared statistic assesses item–trait interaction; nonsignificance indicates a good fit to the Rasch model (p>0.05). The mean person and item fit residuals are item–person interaction statistics that are z-transformed; a good fit to the Rasch model is when they approximate to a mean±sd of 0±1. The PSI assesses how well BHQ discriminates subjects with differing levels of health status. Cronbach's α coefficient is a measure of internal reliability. A PSI and Cronbach's α coefficient ≥0.7 is considered acceptable.