Table 2.

NSAD Psychometric Evaluation Summary Using Rasch Mathematical Methods^a

Parameter	Data
Item fit, mean (SD)	−0.63 (2.01)
Person fit, mean (SD)	−0.28 (0.93)
Reliability (PSI with extremes)	0.96
Ordered thresholds	27/29 (97%)
No. of items with good fitb	23/29
Dependency (no. of pairs)	9
Unidimensionality	Acceptable (t test = 0.037; 95% CI = 0.006–0.069)

^a NSAD = North Star Assessment for limb-girdle type muscular dystrophies; PSI = Person Separation Index.

^b Defined as a fit residual inside the recommended range (−2.50 to +2.50). Three of the 6 misfitting items had significant χ² probability (P < .01).