Psychometric properties of the Greek NEI-RQL-42.

PURPOSE

To evaluate the psychometric properties of the Greek National Eye Institute Refractive Error Quality of Life Questionnaire (NEI-RQL-42).

METHODS

We developed the Greek version of the instrument using forward and backward translation. To examine reliability, Cronbach alpha for each subscale was used as an index of internal consistency. Test-retest reliability was evaluated with intraclass correlation coefficients (ICC). Regarding construct validity, both convergent and discriminant validities were calculated by means of multi-trait analysis. Furthermore, the instrument was evaluated by Rasch analysis, as well.

RESULTS

Three patient groups were studied (emmetropes (n = 20), myopes (n = 41), and hyperopes (n = 18)). Emmetropes scored significantly better in the majority of subscales, while myopes scored better than hyperopes in clarity of vision (p = 0.012), near vision (p<0.001), and satisfaction with correction (p = 0.001). Cronbach alpha ranged from 0.490 (glare) to 0.948 (expectations), with most subscales having high internal consistency. The ICCs ranged from 0.76 to 0.93 for all subscales. All items passed the convergent and discriminant validity tests. Strong correlations were detected between uncorrected visual acuity and near vision, expectations, activity limitations, dependence on correction, worry, and suboptimal correction subscales. Rasch analysis revealed potential weaknesses of the instrument that are associated with the assumptions of the model itself. Specifically, 3 items and 17.5% of the participants fell outside the tolerance box. Moreover, principal component analysis indicated average unidimensionality for the instrument.

CONCLUSIONS

Traditional validation methods indicate that the Greek NEI-RQL-42 scale has adequate psychometric properties for comparative studies in local populations. Rasch analysis indicates significant misfits to the model that should be taken into consideration and evaluated in future studies. These misfits might reflect inherent weaknesses of the original NEI-RQL-42 and not of its adaptation to Greek norms.