Table 2 Overall fit statistics for the DSWAL-QoL scale
Analysis | Item-person interaction | Item-trait interaction | Reliability | Unidimensionality | % ext | |||
|---|---|---|---|---|---|---|---|---|
Scale | Initial scale (# items) Rescaled scale (suggestions by the Rasch model to improve model fit) (# items after adjustments) | Item FR Mean (SD) | Person FR Mean (SD) | χ 2 (df) | p | PSI +ext/÷ext | t-test %, (95% CI) |  |
Total scale | IS Total scale (44) | 0.43 (1.80) | 0.18 (1.62) | 181.03 (44) | <0.001 | 0.93/0.93 | 16.09 (10.9-19.2) | 0 |
RS Total scale (rescore 41 items, delete 6 misfit items) (38) | 0.03 (1.11) | −0.28 (1.87) | 55.47 (38) | 0.032 | 0.93/0.93 | 15.24 (11.1-19.4) | 0.9 | |
General burden | IS General burden (2) | 0.33 (0.15) | −0.49 (1.0) | 3.37 (2) | 0.185 | 0.33/-0.61 | NA | 39.8 |
RS General burden (rescore 2 items) (2) | 0.70 (0.17) | −0.88 (1.66) | 0.49 (2) | 0.782 | 0.17/-2.64 | NA | 65.0 | |
Eating duration | IS Eating duration (2) | 0.39 (0.29) | −0.32 (1.05) | 4.38 (2) | 0.112 | 0.18/-1.32 | NA | 45.1 |
RS Eating duration (rescore 2 items) (2) | 0.96 (0.29) | −1.59 (3.00) | 3.82 (2) | 0.148 | −0.10/-3.47 | NA | 52.9 | |
Eating desire | IS Eating desire (3) | 1.08 (0.72) | −0.10 (1.46) | 8.74 (3) | 0.033 | 0.13/-0.51 | NA | 30.8 |
RS Eating desire (rescore 3 items) (3) | 1.11 (0.56) | −0.73 (2.72) | 8.85 (3) | 0.031 | 0.28/-0.69 | NA | 30.8 | |
Symptoms | IS Symptoms (14) | 0.04 (0.94) | −0.17 (1.16) | 13.66 (14) | 0.475 | 0.83/0.84 | 9.3 (4.9-13.4) | 6.6 |
RS Symptoms (rescore 11 items) (14) | 0.01 (1.05) | −0.21 (1.07) | 18.91 (14) | 0.168 | 0.85/0.84 | 8.2 (3.8-12.6) | 6.6 | |
Food selection | IS Food selection (2) | 0.21 (0.04) | −0.39 (0.66) | 2.96 (2) | 0.227 | 0.46/0.20 | NA | 40.6 |
RS Food selection (rescore 2 items) (2) | 0.47 (0.21) | −0.70 (1.28) | 0.77 (2) | 0.682 | 0.54/0.25 | NA | 40.6 | |
Communication | IS Communication (2) | 0.41 (0.06) | −0.70 (1.06) | 0.19 (2) | 0.908 | 0.77/0.48 | NA | 35.6 |
Fear of eating | IS Fear of eating (4) | 0.32 (0.96) | −0.30 (1.14) | 16.90 (4) | 0.002 | 0.55/0.41 | NA | 25.5 |
RS Fear of eating (rescore 4 items, DIF-split 1 item) (5) | 0.17 (0.92) | −0.45 (1.22) | 8.05 (5) | 0.153 | 0.54/0.38 | NA | 25.5 | |
Mental health | IS Mental health (5) | 0.20 (0.76) | −0.41 (1.35) | 4.45 (5) | 0.487 | 0.75/0.75 | NA | 30.5 |
RS Mental health (rescore 1 item) (5) | 0.26 (0.79) | −0.37 (1.23) | 2.33 (5) | 0.801 | 0.74/0.74 | NA | 30.5 | |
Social functioning | IS Social functioning (5) | 0.17 (0.64) | −0.41 (1.17) | 5.09 (5) | 0.405 | 0.72/0.59 | NA | 31.1 |
RS Social functioning (rescore 5 items) (5) | 0.40 (0.92) | −0.39 (1.44) | 8.19 (5) | 0.146 | 0.72/0.44 | NA | 36.8 | |
Fatigue | IS Fatigue (3) | 0.50 (0.11) | −0.52 (1.10) | 2.30 (3) | 0.513 | 0.69/0.56 | NA | 20.8 |
RS Fatigue (rescore 3 items) (3) | 0.49 (0.23) | −0.26 (0.88) | 1.27 (3) | 0.737 | 0.61/0.38 | NA | 30.2 | |
Sleep | IS Sleep (2) | 0.86 (0.06) | −0.54 (1.22) | 2.13 (2) | 0.345 | 0.27/-0.88 | NA | 43.4 |
RS Sleep (rescore 2 items) (2) | 0.47 (0.05) | −1.63 (1.90) | 0.63 (2) | 0.729 | 0.17/-2.40 | NA | 43.4 | |
Satisfactory fit | 0.00 (<1.40) | 0.00 (<1.40) |  | >0.05 | ≥0.70 | <5% or LCI ≤5% |  | |