Table 4

Rasch analysis for the Dyspnoea-12 (n=203)

Scale/item (overall fit p value*)	Location†	Fit residual	χ2	P value	PSI‡, Cronbach’s alpha
Physical function (0.85)					0.89, 0.92
My breath does not go all the way in	−0.32	1.29	2.50	0.29
My breathing requires more work	0.15	−1.56	3.73	0.16
I feel short of breath	−1.38	0.62	0.07	0.97
I have difficulty catching my breath	0.43	−0.38	0.97	0.62
I cannot get enough air	−0.75	0.26	0.25	0.88
My breathing is uncomfortable	0.90	−0.87	0.71	0.70
My breathing is exhausting	0.33	0.40	0.55	0.76
Affective (0.31)					0.89, 0.93
My breathing makes me feel depressed	0.17	−1.84	2.74	0.25
My breathing makes me feel miserable	0.22	−2.15	3.93	0.14
My breathing is distressing	−0.31	0.40	0.30	0.86
My breathing makes me agitated	0.84	−0.62	0.31	0.86
My breathing is irritating	−0.91	3.15	4.35	0.11

*Overall fit p- value for χ2, where a non-significance (p>0.05) indicates fit to the Rasch model.
†Location is the item position on the latent scale or level of health assessed. Fit residuals are the difference between the observed and scores for the item and χ2 where a non-significance (p>0.05) indicates fit to the Rasch model.
‡Person Separation Index is an estimate of reliability or the proportion of error free variance of the distribution of person estimates relative to the sum of this variance and the error variance in these estimates.