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

To evaluate the reliability of self-reported dry eye disease status and patient-related predictors of misclassification in contact lens wearers.

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.

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.

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.