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Fig. 2 | BMC Medical Research Methodology

Fig. 2

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

Fig. 2

Interpretation of the (cumulative,logistic, Z 1,U 2 ) model through its underlying latent variable concerning the pain symptom (including the items 9 and 19). The estimated difficulty parameter for the item 9 are δ 9,1=−2.1, δ 9,2=1 and δ 9,3=2.75, and for the item 19 : δ 19,1=−1.28, δ 19,2=1.40 and δ 19,3=3.34. a the different HRQoL evolution of the latent variable and response variable (Y (j)) j=9,19 between the two groups. b the different proportions (π m ) of different response categories of Y (9) between the two groups four months after the Baseline (t 4)

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