I have ordinal data from 2 questionnaires. One questionnaire has a scale of 1:7 and the other of 1:5. I would like to convert these data to interval using polytomous item response theory. I can calculate the thresholds and draw the plots, but don't understand how to use this data to convert my raw ordinal data into interval data.
df = data.frame("Q1" = sample(1:7, 100, replace = T), "Q2" = sample(1:5, 100, replace = T)) library(mirt) model = mirt(data = df, model = 1, itemtype = "gpcm") coef(model, IRTpars = T) plot(model, type = "trace")