Hello everyone,

I am trying to undertake an item bifactor analysis of graded response data from a questionnaire. I am using the mirt package, especially the bfactor function.My dataset is called "data.items", it contains about 2000 observations and 31 variables (variables represent the items in the questionnaire). The items follow a Likert scale format and represent a level of satisfaction, missing values are coded as NA). I am having trouble at the beginning of my analysis, during the exploratory model fitting. The syntax and the error message are as follows:

> bfactor(data.items,model=9)
Error in ESTIMATION(data = data, model = model, group = rep("all", nrow(data)),  : 
  index out of bounds

I get the same error when i try with: bfactor(data.items,9,itemtype="graded") or  bfactor(data.items,9,prev.cor=cor)
where cor is the correlationmatrix that i compute without the missing values.

If someone have an idea to suggest, do not hesitate.

Thank you.

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