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Table 3 Data quality, scaling assumptions, targeting, reliability and validity

From: The Cervical Dystonia Impact Profile (CDIP-58): Can a Rasch developed patient reported outcome measure satisfy traditional psychometric criteria?

CDIP Scale Head and
Neck
Symptoms
(6 items)
Pain and
Discomfort
(5 items)
Upper
Limb
Activities
(9 items)
Walking
(9 items)
Sleep
(4 items)
Annoyance
(8 items)
Mood
(7 items)
Psycho-
social
Functioning
(10 items)
Psychometric property         
Data quality         
   Item missing data (range %) 1–2 3–4 2–4 3–4 2 2–4 2–4 1–2
   Computable scale scores (%) 98 97 98 97 98 98 96 99
Corrected item-total correlations         
   Mean 0.76 0.82 0.78 0.87 0.89 0.83 0.78 0.82
   Range 0.67–0.81 0.70–0.87 0.64–0.87 0.82–0.91 0.84–0.93 0.79–0.89 0.68–0.84 0.70–0.90
Item-other scale correlations         
   Range 0.37–0.72 0.40–0.75 0.43–0.72 0.42–0.75 0.39–0.52 0.42–0.73 0.39–0.82 0.38–0.69
Scaling successes (%) 83 80 100 100 100 100 86 100
   Targeting         
   Mean score 57.6 53.8 42.9 37.1 33.3 37.9 29.7 49.2
   Standard deviation 25.6 27.9 27.6 31.5 31.5 26.9 24.9 29.5
   Score range 0–100 0–100 0–100 0–100 0–100 0–100 0–100 0–100
   Floor/ceiling effect (%) 1/6 2/7 7/0 17/4 27/7 7/4 13/1 5/4
Skewness -0.23 -0.15 0.11 0.44 0.66 0.51 0.82 0.02
Reliability (n = 377–385)         
Cronbach's alpha 0.92 0.93 0.94 0.97 0.96 0.96 0.95 0.96
TRT (ICC; n = 92–95) 0.85 0.83 0.94 0.95 0.86 0.83 0.85 0.89