Table 2.

Summary measures of Rasch model fit in the subset of patients selected to ensure equal precision across the scale (n = 491)^*

	Location	SE	Residuals	χ2	P	F†	P
Item
1. Walking	−0.054	0.070	0.233	3.19	0.921	0.48	0.872
2. On stairs	−1.048	0.072	0.253	9.38	0.311	1.48	0.163
3. In bed	0.339	0.067	1.996	9.55	0.298	1.24	0.276
4. Lying/sitting	0.540	0.070	−0.534	12.83	0.118	2.03	0.041
5. Standing	0.223	0.070	−1.115	8.36	0.399	1.53	0.145
Mean ± SD	0.000 ± 0.624		0.167 ± 1.172
Persons
Mean ± SD	−0.270 ± 2.451		−0.445 ± 1.160
Model fit
Item–trait interaction PSI = 0.90/0.89‡				43.31	0.332

^*PSI = person separation index.

^†For analysis of variance F statistic.

^‡Excluding individuals with “extreme” scores (at the very top or bottom of the range).