Table 2.
Associations between IRT-derived disability scores and prevalence of unemployment after adjustment for patient characteristics
| Characteristic | Bifactor model | Unidimensional model | ||
|---|---|---|---|---|
| N (%) | PR a (95% CI) | PR a (95% CI) | PR a (95% CI) | |
| Global disability (scaled score, S)b | ||||
| S ≤ 33.3 | 562 (14.3) | 1.0c,d | 1.0c,d | 1.0c,e |
| 33.3 < S ≤ 50 | 1390 (35.4) | 1.50 (1.28, 1.77) | 1.83 (1.55, 2.17) | 1.73 (1.46, 2.04) |
| 50 < S ≤ 66.7 | 1428 (36.4) | 2.14 (1.83, 2.51) | 2.75 (2.34, 3.23) | 2.87 (2.46, 3.36) |
| S > 66.7 | 546 (13.9) | 2.74 (2.33, 3.22) | 3.66 (3.12, 4.30) | 3.79 (3.24, 4.43) |
| Residual physical disability (scaled score, S)b | ||||
| S ≤ 33.3 | 257 (6.5) | 1.0c,d | ||
| 33.3 < S ≤ 50 | 1876 (47.8) | 1.17 (.99, 1.38) | ||
| 50 < S ≤ 66.7 | 1339 (34.1) | 1.56 (1.32, 1.84) | ||
| S > 66.7 | 454 (11.6) | 2.02 (1.70, 2.40) | ||
| Residual mental disability (scaled score, S)b | ||||
| S ≤ 33.3 | 236 (6.0) | 1.0c,d | ||
| 33.3 < S ≤ 50 | 1678 (42.7) | 1.11 (.98, 1.26) | ||
| 50 < S ≤ 66.7 | 1783 (45.5) | 1.35 (1.19, 1.52) | ||
| S > 66.7 | 229 (5.8) | 1.53 (1.32, 1.78) | ||
| Disease duration (y.) | ||||
| ≤ 10 | 1713 (43.6) | 1.0c | 1.0c | 1.0c |
| 11 – 20 | 1109 (28.3) | 1.06 (.98, 1.14) | 1.10 (1.02, 1.19) | 1.09 (1.01, 1.18) |
| ≥ 21 | 1104 (28.1) | 1.21 (1.13, 1.30) | 1.27 (1.18, 1.37) | 1.25 (1.16, 1.34) |
| Age at assessment (y.) | ||||
| ≤ 35 | 749 (19.1) | 1.0c | 1.0c | 1.0c |
| 36 – 55 | 1760 (44.8) | 1.01 (.91, 1.11) | 1.03 (.93, 1.14) | 1.02 (.92, 1.13) |
| ≥ 56 | 1417 (36.1) | 1.22 (1.10, 1.35) | 1.31 (1.18, 1.45) | 1.28 (1.16, 1.42) |
| Gender | ||||
| Female | 3102 (79.4) | 1.0c | 1.0c | 1.0c |
| Male | 803 (20.6) | 1.04 (.98, 1.10) | 1.08 (1.02, 1.15) | 1.08 (1.01, 1.14) |
| Race/Ethnicity | ||||
| White | 3491 (90.2) | 1.0c | 1.0c | 1.0c |
| African American | 132 (3.4) | 1.14 (.99, 1.31) | 1.16 (1.00, 1.33) | 1.14 (.99, 1.31) |
| Hispanic/Latino | 120 (3.1) | 1.14 (.97, 1.34) | 1.11 (.95, 1.31) | 1.12 (.94, 1.31) |
| Native American | 76 (2.0) | 1.11 (.95, 1.30) | 1.10 (.95, 1.28) | 1.09 (.94, 1.25) |
| Other | 49 (1.3) | 1.23 (1.00, 1.52) | 1.24 (1.00, 1.52) | 1.16 (.94, 1.43) |
| Disease modifying therapy | ||||
| Yes | 2614 (66.6) | 1.0c | 1.0c | 1.0c |
| No | 1312 (33.4) | 1.05 (.99, 1.11) | 1.08 (1.02, 1.14) | 1.06 (1.01, 1.13) |
| Year of assessment | ||||
| 2003-2005 | 1640 (41.8) | 1.0c | 1.0c | 1.0c |
| 2006-2008 | 957 (24.4) | 1.01 (.94, 1.08) | 1.01 (.94, 1.09) | 1.02 (.95, 1.09) |
| 2009-2011 | 1329 (33.8) | 1.04 (.98, 1.11) | 1.01 (.94, 1.07) | 1.01 (.95, 1.08) |
aPR stands for “prevalence ratio”. Because prevalence of unemployment was high, we performed Poisson regression with robust variance estimation instead of logistic regression to obtain unbiased prevalence ratio estimates [30].
bIRT scores scaled to have mean 50 and SD 15 in the NARCOMS sample.
cReference category.
dBayesian Expected a posteriori (EAP) estimates of disability (i.e., “IRT pattern scores”).
eEAP summed-score estimates of disability (i.e., “IRT summed scores”).