I am trying to predict the length oh hospital stay based on participants’ responses to a depression questionnaire. The questionnaire consists of 10 items to which participants respond on a likert scale from 1 to 5.
Normally I would add the items on a likert scale up and use a single score for each person. However, I recently read this article https://journals.sagepub.com/doi/10.1177/2515245918823199 and would like to do this properly taking into account all items. However, I have never used this kind of analysis before, and I struggle to adapt these recommendations to a situation where multiple likert items are used.
I defined the model as this:
brm( formula = HospitalStay ~ 1 + ResponseToDepressionQuestionnaire + (1 | Participant) + (1 | ItemOftheQuestionnaire), family = cumulative, data = depression )
Data is in long format with 10 rows for each participant.
Could anyone please help me and check that this is correct? Is there anything else that I need to add?