Validity and Reliability of the Glaucoma Knowledge Level Questionnaire

Abstract

Objectives: The present study was conducted to develop an instrument for measuring adults’ glaucoma knowledge levels and toestablish the instrument’s validity and reliability.Materials and Methods: The study group consisted of 811 persons aged 40-80 years who presented to primary health care institutionsand did not have a glaucoma diagnosis. A 27-item questionnaire measuring level of glaucoma knowledge was created by the study team.Following expert consultation, it was structurally evaluated. The difficulty index and discrimination index were calculated for each item.Factor analysis was used to determine construct validity, Cronbach’s alpha internal consistency coefficient and item-total correlationswere calculated to determine reliability. Confirmatory factor analysis was used to assess the extent to which the factor structure of thescale fit. We analysed correlation with the National Eye Health Education Program (NEHEP) Eye-Q scale in order to evaluate thevalidity of the scale.Results: The final glaucoma knowledge level questionnaire comprised 10 items in one dimension. The discrimination index anddifficulty index ranged between 0.28 to 0.65 and 33 to 61%, respectively. According to factor analysis, the Kaiser-Meyer-Olkin score was0.760 and Bartlett’s test indicated p