Adult Strabismus-20 questionnaire (AS-20) before (left, 5 categories) and after (centre, 4 categories, and right, 3 categories) the collapsing procedure.

Cat. label—Category label; Obs. Count: Observed count—number of times each response category was used across items and participants in percentage; Avg. measure: Average measure—mean ability of the participants getting a given score; Step calib.—Step calibrations or Rasch/Andrich thresholds correspond to the ability level at which adjacent scores are equally likely

^ϮNo threshold presented for category 0 because it is the lowest category.

Adult Strabismus-20 questionnaire (AS-20) before (left, 5 categories) and after (centre, 4 categories, and right, 3 categories) the collapsing procedure.