Rasch-calibrated Intermittent Exotropia Symptom Questionnaire for Children

Abstract

Significance: A rigorously designed and calibrated symptom questionnaire for childhood intermittent exotropia would be useful for clinical care and for research.

Purpose: The aim of this study was to Rasch-calibrate and evaluate the previously developed Child Intermittent Exotropia Symptom Questionnaire using data gathered as part of a randomized clinical trial.

Methods: The questionnaire was administered to 386 children aged 3 to 10 years with intermittent exotropia who were enrolled in a randomized clinical trial comparing overminus with nonoverminus spectacles. Participants were followed at 6 and 12 months while on treatment and at 18 months off treatment. Factor analysis determined dimensionality, and Rasch analysis evaluated questionnaire performance. Logit values were converted to 0 (best) to 100 (worst). We evaluated differences in questionnaire scores between treatment groups and time points, and correlations with control scores.

Results: The Child Intermittent Exotropia Symptom Questionnaire was unidimensional. Rasch analysis indicated that there was no notable local dependence and no significant differential item functioning for sex or age. There was suboptimal targeting (mean logit, -1.62), and person separation was somewhat poor (0.95). There were no significant differences in the Child Intermittent Exotropia Symptom score between overminus spectacles and nonoverminus spectacles at 6, 12, and 18 months. Combining data from both treatment groups, there was significant improvement from baseline at all follow-up visits (e.g., mean change from baseline to 12 months, -6.6 points; 95% confidence interval, -8.6 to -4.6). Child Intermittent Exotropia Symptom scores were not correlated with distance or near control scores at 12 months.

Conclusions: The seven-item Rasch-scored Child Intermittent Exotropia Symptom Questionnaire is limited by suboptimal performance. Future study is needed to determine whether it may be useful for clinical practice and for research.

Trial registration: ClinicalTrials.gov NCT02807350.

Figure 1.

Child Intermittent Exotropia Symptom Questionnaire. The 7-item questionnaire was administered to children ages 3 to <7 years by study personnel or self-administered by children 7 to 10 years old, with assistance from study personnel if needed. Response options for each question were “never,” “sometimes,” and “all the time.”

Figure 2.

Category Thresholds / Category Probability Curves. Category threshold / category probability curves illustrate proper ordering of response categories and utilization of response options.

Figure 3.

Targeting of the Child Intermittent Exotropia (IXT) Symptom Questionnaire. Targeting was suboptimal for the Child IXT Symptom Questionnaire, noting position of mean (M) of respondents on left of figure and questions on right of figure (mean difference −1.62 logits).

Figure 4.

Relationship of Child Intermittent Exotropia (IXT) Symptom Score with Distance Control at 12 Months. Scatter plot of distance control at 12 months versus child IXT symptom score at 12 months. The Spearman correlation coefficient, calculated on the logit scale, was −0.04 (95% CI −0.15, 0.07), indicating no correlation; results were similar at all other visits.

Figure 5.

Relationship of Child Intermittent Exotropia (IXT) Symptom Score with Near Control at 12 Months.Scatter plot of near control at 12 months versus child IXT symptom score at 12 months. The Spearman correlation coefficient, calculated on the logit scale, was 0.08 (95% CI −0.03, 0.18), indicating no correlation; results were similar for other visits.