I have some items, measured with 5-point Likert scale (e.g., Strongly Agree, Agree, Neutral, Disagree, Strongly Disagree), to model using Graded Response Model. However, the analysis runs extremely slow. Further analysis showed that some categories are answered with sample size less than 5. I wonder if it is appropriate to collapse/combine some response categories, so that it becomes a 3-point Likert scale (e.g., Agree, Neutral, Disagree)? Does the field reject this practice in general?
Some references to this issue will be useful. Thanks!