Table 3.

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

	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. Covariance in upper triangle, correlation coefficient in lower triangle; variance along the diagonal line.

2. Skew_ Exp: skewness with expected scores; Skew_ Obs: skewness with observed scores