VALIDATION DATA

Cronbach's alpha value ranged from 0.88 to 1.00.

Reliability coefficients observed for the satisfaction with role performance (r = 0.86) and experienced physical difficulties (r = 0.91) scales suggest a high degree of internal consistency given that both dimensions now have only 6 items.

For s-SRPQ/experienced physical difficulties; the individual item ICC ranged from 0.78 to 1.00 and for s-SRPQ/satisfaction with role performance; the individual item ICC ranged from 0.93 to 0.98

The reliability of both versions of the SRPQ across 3 dimensions of participation was evaluated with an IRT-based index of reliability.

The conclusion of the IRT analysis was that the multidimensional  generalized partial credit model adequately described the response data for all 3 dimensions of the SRPQ. The correlation between the “experienced physical difficulties” with “satisfaction with time spent in roles” and “satisfaction with role performance” dimensions was r = 0.51 and r = 0.71, respectively. The correlation between both satisfaction dimensions was r = 0.91. The very high correlation between both satisfaction dimensions observed in the IRT analysis suggested that these scales provided very little unique information about the effect of the disease in functioning in AS. Because the dimension “satisfaction with performance” had higher face validity, we considered this “satisfaction” dimension only in the s-SRPQ. Therefore, no further results will be presented for the “satisfaction with time spent in roles” dimension.

Construct validity of the s-SRPQ was found comparable to the original as evidenced by a similar pattern of correlations of both dimensions of the s-SRPQ with SF-36 and SWLS.

Moderate to strong correlations with SF-36 subscales and SWLS were observed in all cases. More specifically for our study, correlation coefficients were within only a 0.05-point difference in all cases, except for the correlation with SF-36 vitality scale, which showed a stronger correlation with the experienceddifficulties subscale of the short form compared with the original SRPQ.

Generally, mean scores were similar for the original SRPQ and the s-SRPQ, while SD were slightly higher for the s-SRPQ scales.