Table 1.
Item content of the Adult Strabismus Questionnaire-20*.
Table 2.
Characteristics of the 584 participants who completed the Adult Strabismus-20 Questionnaire.
Fig 1.
Rasch model category probability curves for all items together in the AS-20 showing the likelihood that a participant with a particular coping ability will select a category.
A. The scale (x-axis) from +6 to -6 symbolizes the latent trait of health-related quality of life and the y-axis represents the probability of category being selected. Response categories: 0 “never”, 1 “rarely”, 2 “sometimes”, 3 “often” and 4 “always”. For any given point along this scale, the category most likely to be chosen by a participant is shown by the category curve with the highest probability. At no point, was category 1 the most likely to be chosen and appears to be interchangeable with categories 0 and 2, resulting in disordered thresholds. B. Ordered thresholds following category re-organization and reducing the number of categories from 5 to 3 for the category probability curves seen in Fig A. Thresholds represent boundaries along the scale where the probability of a response category being chosen changes from one to the next.
Table 3.
Adult Strabismus-20 questionnaire (AS-20) before (left, 5 categories) and after (centre, 4 categories, and right, 3 categories) the collapsing procedure.
Fig 2.
Person-item map for the Rasch-revised 8-item ‘psychosocial’ subscale of the AS-20 questionnaire.
Participants are located on the left of the dashed line (represented by ‘x’) and participants with worse health-related quality of life are located at the top of the map. Items are on the right of the dashed line with those considered to be less difficult to endorse are located toward the top of the map. Each ‘x’ and “.” represent four and one participants respectively. Alongside each item is also indicated its original item number as in the AS-20 questionnaire. The complete description of items can be found in Table 1 in the text. M, mean; S, 1 SD from the mean; T, 2 SD from the mean.
Table 4.
Overall performance of the AS-20 and its two subscales in adults with strabismus.
Fig 3.
Person-item map for the Rasch-revised 9-item ‘function’ subscale of the AS-20 questionnaire.
Participants are located on the left of the dashed line (represented by ‘x’) and participants with worse health-related quality of life are located at the top of the map. Items are on the right of the dashed line with those considered to be less difficult to endorse are located toward the top of the map. Each ‘x’ and “.” represent six and one participants respectively. Alongside each item is also indicated its original item number as in the AS-20 questionnaire. The complete description of items can be found in Table 1 in the text. M, mean; S, 1 SD from the mean; T, 2 SD from the mean.