An assessment of self-reported disease classification in epidemiological studies of dry eye.

PURPOSE To evaluate the reliability of self-reported dry eye disease status and patient-related predictors of misclassification in contact lens wearers. METHODS Patients completed the Contact Lens Dry Eye Questionnaire (CLDEQ) short form on two occasions. Test-retest reliability of the CLDEQ composite score was determined using the 95% limits of agreement (LoA) and an intraclass correlation coefficient (ICC). The kappa statistic was used to determine reliability of disease-classification-based CLDEQ composite score cutoff points. Predictors of misclassification were determined by multivariate logistic regression. RESULTS The sample included 274 patients. The range of CLDEQ composite scores from both visits was -1.83 to 4.50 and the mean difference between administrations was -0.05 +/- 0.75 (P = 0.30). The 95% LoA of the CLDEQ composite score were -1.51 to 1.42 and the ICC was 0.61 (95% confidence interval [CI]: 0.53-0.68). Calculations using the lower limit of the 95% CI showed that three administrations of the survey would be required to obtain a more desirable ICC (0.70). The kappa statistic for reliability of dry eye disease classification was 0.58 (95% CI: 0.48-0.67). Logistic regression showed a significant interaction between gender (females) and younger age (P = 0.02) in relation to misclassification of self-reported dry eye disease status. CONCLUSIONS The reliability of self-reported dry eye disease classification in contact lens wearers is moderate. In epidemiologic studies of factors associated with self-reported disease status, investigators may be well advised to consider using multiple administers of such outcome instruments and controlling for sociodemographic characteristics to maintain internal validity.