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Table 3 Relationship between items among difficulty (logit), skewness, observed scores and expected scores (item number = 28).

From: Reliability of 95% confidence interval revealed by expected quality-of-life scores: an example of nasopharyngeal carcinoma patients after radiotherapy using EORTC QLQ-C 30

 

Difficulty

Skew_ Exp.

Observed

Expected

Skew_ Obs.

Difficulty

0.72

0.55

-21.72

-20.93

0.64

Skew_Exp.

0.95

0.46

-16.03

-16.07

0.51

Observed

-0.98

-0.90

684.07

656.29

-18.28

Expected

-0.97

-0.93

0.98

650.99

-17.58

Skew_Obs.

0.95

0.94

-0.88

-0.87

0.63

  1. 1. Covariance in upper triangle, correlation coefficient in lower triangle; variance along the diagonal line.
  2. 2. Skew_ Exp: skewness with expected scores; Skew_ Obs: skewness with observed scores