Figure 2

a–e Rasch model category probability curves showing functional rating scales for items with five response categories that assess ‘difficulty’ in five different questionnaires: (a) Visual Symptoms and Quality of Life Questionnaire, VSQ (Question numbers 1, 6, 8 and 9). Response categories of 1–5 correspond to ‘no difficulty’, ‘yes, a little difficulty’, ‘yes, some difficulty’, ‘yes, a great deal of difficulty’ and ‘I cannot perform the activity because of my eyesight’. (b) Cataract Symptom Scale, CSS (all). Response categories of 0–4 correspond to ‘no’, ‘a little difficulty’, ‘a moderate difficulty’, ‘very difficult’ and ‘unable to do’. (c) Technology of Patient Experiences (Question numbers 2–13). Response categories of 1–5 correspond to ‘not at all’, ‘a little bit’, ‘some’, ‘quite a lot’, and ‘totally disabled’. (d) Visual Function-14, VF-14 (all). Response categories of 0–4 include ‘unable to do the activity’, ‘a great deal, ‘a moderate amount’, ‘a little’ and ‘no’. (e) National Eye Institute –Visual Function Questionnaire NEIVFQ (Question numbers 5–16). Response categories of 1–5 include ‘no difficulty at all’, ‘a little difficulty’, ‘moderate difficulty’, ‘extreme difficulty’ and ‘stopped doing this because of eyesight’. Figure 2 (f) Rasch model category probability curves showing disordered thresholds for five- response category questions that assess ‘difficulty’ in Activities of Daily Living Scale (ADVS). The peak of the two middle categories 2 and 3 are submerged and the thresholds are disordered which represents that the respondents had difficulty discriminating adjacent categories.