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Table 4 Overall fit statistics for the aDSWAL-QoL scale

From: Validation of the Dutch version of the Swallowing Quality-of-Life Questionnaire (DSWAL-QoL) and the adjusted DSWAL-QoL (aDSWAL-QoL) using item analysis with the Rasch model: a pilot study

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)
χ2 (df) p PSI
+ext/÷ ext
t-test
%, (95%CI)
 
Total scale IS Total scale (44) 0.19 (1.95) −0.01 (1.64) 302.65 (44) <0.001 0.93/0.93 17.59 (13.5-21.7) 0
RS Total scale (rescore 43 items, delete 7 misfit items, DIF-split 5 items) (42) −0.19 (0.95) −0.46 (1.86) 50.96 (42) 0.137 0.92/0.92 NA 0
General burden IS General burden (2) 0.17 (0.10) −0.57 (0.86) 1.58 (2) 0.453 0.69/0.51 NA 38.9
Eating duration IS Eating duration (2) −0.12 (0.32) −0.29 (0.62) 3.95 (2) 0.139 0.70/0.42 NA 24.5
RS Eating duration (rescore 1 item + DIF-split 1 item) (3) 0.06 (0.16) −0.29 (0.60) 2.70 (3) 0.440 0.68/0.37 NA 24.5
Eating desire IS Eating desire (3) 0.32 (0.51) −0.24 (0.80) 6.17 (3) 0.104 0.61/0.40 NA 2.8
RS Eating desire (rescore 3 items) (3) 0.37 (0.35) −0.22 (0.73) 10.75 (3) 0.013 0.57/0.32 NA 10.2
Symptoms IS Symptoms (14) −0.05 (0.88) −0.29 (1.25) 10.23 (14) 0.741 0.87/0.86 10.8 (6.6-15.0) 2.8
RS Symptoms (rescore 9 items) (14) −0.08 (0.64) −0.29 (1.17) 12.02 (14) 0.605 0.86/0.85 11.8 (7.5-16.0) 2.8
Food selection IS Food selection (2) 0.74 (0.77) −0.10 (0.67) 5.21 (2) 0.074 −0.44/-1.31 NA 29.9
RS Food selection (rescore 2 items) (2) 0.82 (0.78) −0.10 (0.55) 1.11 (2) 0.574 −0.39/-1.33 NA 29.9
Communication IS Communication (2) 0.25 (0.24) −1.09 (1.57) 2.44 (2) 0.295 0.46/0.18 NA 18.1
RS Communication (rescore 1 item) (2) 0.39 (1.47) −1.14 (1.89) 1.12 (2) 0.570 0.43/-0.03 NA 27.6
Fear of eating IS Fear of eating (4) 0.82 (1.65) −0.36 (1.37) 57.75 (4) <0.001 0.26/0.23 NA 3.8
RS Fear of eating (rescore 2 items + delete 1 misfit item) (3) 0.66 (0.58) −0.19 (1.06) 7.01 (3) 0.072 0.15/-0.31 NA 38.6
Mental health IS Mental health (5) −0.02 (0.83) −0.48 (1.20) 4.46 (5) 0.486 0.71/0.72 NA 22.6
RS Mental health (rescore 4 items) (5) 0.08 (0.91) −0.41 (1.02) 6.66 (5) 0.247 0.73/0.72 NA 24.5
Social functioning IS Social functioning (5) 0.08 (0.70) −0.24 (0.96) 11.93 (5) 0.036 0.50/0.39 NA 31.8
RS Social functioning (rescore 5 items) (5) 0.35 (0.81) −0.49 (1.49) 3.801 (5) 0.578 0.62/0.46 NA 31.8
Fatigue IS Fatigue (3) 0.12 (0.66) −0.49 (1.03) 1.64 (3) 0.651 0.70/0.60 NA 14.3
Sleep IS Sleep (2) 0.37 (0.10) −0.38 (0.82) 3.15 (2) 0.207 0.43/0.03 NA 29.5
RS Sleep (rescore 1 item) (2) 0.13 (1.40) −0.29 (0.72) 2.50 (2) 0.287 0.39/-0.06 NA 35.2
Satisfactory fit 0.00 (<1.40) 0.00 (<1.40)   >0.05 ≥0.70 <5% or LCI ≤5%  
  1. Abbreviations and symbols: aDSWAL-QoL adjusted DSWAL-QoL, IS initial scale, RS rescaled scale based on the suggestions from the Rasch methodology, DIF differential item functioning, FR fit residual, SD standard deviation, PSI Person separation index reported with extremes (+) and without extremes (÷), χ 2 (df) chi-square (degrees of freedom), LCI lower confidence interval, % ext percentage of extreme scores, NA not applicable (T-tests were not performed when there were too few thresholds in each subset or when the items were split for DIF when using the RUMM software). Bold indicates misfit to the Rasch model. Bold italic indicates multidimensionality