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Fig. 1 | BMC Medical Research Methodology

Fig. 1

From: Evaluating the impact of calibration of patient-reported outcomes measures on results from randomized clinical trials: a simulation study based on Rasch measurement theory

Fig. 1

Illustration of the archetypes of items distribution, for different scenarios. Legend: Vertical dashed lines represent the item response category thresholds (δjl, with each color corresponding to a different item) in different scenarios, and the probability density function curve represents the distribution of the latent trait in the calibration sample (case with a variance = 1). The left part of the figure includes cases where the item locations δj have a low dispersion (range = 0.5) and the δjl have a high dispersion (SD = 2.5). The right part of the figure includes cases where the item locations δj have a high dispersion (range = 2) and the δjl have a low dispersion (SD = 1.5). Each line corresponds to different scenarios regarding the number of item and modalities: A) J = 4 items, M = 3 modalities. B) J = 4 items, M = 5 modalities. C) J = 10 items, M = 5 modalities. Full values for the response category thresholds δjl are provided in supplementary materials (Additional file 1)

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