Table 2.
Item characteristic curve parameter estimates (% relative standard error) for baseline National Institutes of Health Stroke Scale scores
| j | αj | βj1 | βj2 | βj3 | βj4 |
|---|---|---|---|---|---|
| 1 | 0.443 (46.5) | 4.051 (45.6) | 3.075 (38.5) | 3.851 (42.8) | |
| 2 | 0.183 (97.5) | 11.44 (98.4) | −10.4 (98.8) | ||
| 3 | 0.337 (62.3) | 5.313 (63.6) | −3.064 (70.9) | ||
| 4 | 0.710 (19.0) | 0.172 (123.7) | 0.695 (31.1) | ||
| 5 | 0.454 (23.7) | 3.293 (31.1) | −4.215 (27.6) | 8.39 (25.9) | |
| 6 | 0.991 (20.6) | −1.44 (15.6) | 0.351 (40.6) | 4.367 (19.1) | |
| 7 | 2.864 (49.8) | −1.117 (10.3) | −0.320 (36.9) | −0.493 (59.1) | 0.995 (13.0) |
| 8 | 2.131 (25.3) | −0.918 (13.3) | −0.272 (44.1) | −0.038 (383.6) | 1.656 (10.4) |
| 9 | 0.739 (20.8) | −0.671 (29.5) | 2.928 (16.9) | ||
| 10 | 0.001 FIX | 3989 (7.37) | 0 FIX | ||
| 11 | 0.184 (73.1) | 11.28 (75.4) | −3.935 (88.4) | −3.349 (75.1) | |
| 12 | 0.629 (37.8) | −3.312 (29.6) | −0.104 (200.4) | ||
| 13 | 0.140 (97.2) | 17.51 (98.2) | −10.02 (100.9) |
αj, slope or scale parameter denoting the discrimination power of test j; βjv, test step or intersection parameter denoting the points on the latent trait scale, where the plots of P(Yij = k) and P(Yij = k + 1) intersect, with Yij being a test score; j, test number (j = 1, 2, ... 13), v, category number (v = 1, 2, 3, 4)