Table 2

Summary of Rasch analysis

Rasch statisticsK-BILD domains
PsychologicalBreathlessness and activityChest symptomsTotal score
Number of items74315
χ2 fit statistic18.28.27.941.0
Degrees of freedom148630
p Value0.200.420.250.09
Mean item fit residual (SD)−0.1 (0.9)−0.01 (0.9)0.4 (1.2)0.2 (1.1)
Mean person fit residual (SD)−0.3 (1.1)−0.5 (1.1)−0.5 (1.3)−0.2 (1.2)
Cronbach's α coefficient0.900.900.720.94
  • χ2 statistic assesses item–trait interaction; non-significance 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 Person Separation Index (PSI) assesses how well K-BILD 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.