1. The Presence and Severity may be modeled by two-dimensional IRT model. When presence lacks, the response to severity is missing; otherwise it is observable. Theta 1 presents the propensity trait and theta 2 is the latent trait presenting the severity.
2. I didn’t get the idea clearly why a parameters are interpreted as category severities.
3. Some items’ ICCs is not satisfied. The methodology used in this paper should be in question.
4. Physical and psychological seems inappropriate that be been analyzed in the same model. They may be on different latent scale.