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Table 3 Values of difficulty parameters used to simulate the data and expected responses at t 0 under each studied scenarios

From: Item response models for the longitudinal analysis of health-related quality of life in cancer clinical trials

  Difficulty parameters
Models \(\delta _{1}^{ne}=(-1.6,1,1.45)\) \(\delta _{1}^{fa}=(-2.1,1,2.75)\)
(r,F,Z 1,U a ) a=1,2 \(\delta _{2}^{ne}=(-0.8,1.15,1.9)\) \(\delta _{2}^{fa}=(-1.25,1.4,3.3)\)
(adjacent,logistic, Z 1,U a ) a=1,2 Balanced responses Focus on center categories (1 and 2)
(cumulative,logistic, Z 1,U a ) a=1,2 Focus on extreme categories (0,1 and 3) Balanced responses