title: Validation and cross-cultural adaptation of the National Eye Institute Visual Function Questionnaire (NEI VFQ-25) in Serbian patients.
abstract: OBJECTIVE
  To test the validity and reliability of the Serbian version of the interviewer-administered format of the National Eye Institute Visual Functioning Questionnaire (NEI VFQ-25).
  
  
  METHODS
  The Serbian version of NEI VFQ-25 was translated in accordance with standard methods that have been adopted internationally. In order to assess the reliability and validity of the translated NEI VFQ-25, we used a sample of 105 patients with four different chronic ocular diseases. Cronbach's alpha coefficient was used to assess internal consistency for each subscale. To assess test-retest reliability, intraclass correlation coefficients were used. The test-retest data were obtained from clinically stable patients with age-related cataracts, in surveys performed 2 weeks apart. Rasch analysis was also applied as a modern methods of psychometric assessment of the questionnaire.
  
  
  RESULTS
  Four groups of patients were studied and the most prevalent were patients with cataract 40 (38.1%), followed by diabetic retinopathy 31 (29.5%), age related macular degeneration 22 (21.0%) and glaucoma 12 (11.4%). The overall index score on the NEI VFQ-25 ranged from 65.3 to 67.8 with a mean of 67.4 ± 15.0. Cronbach's alpha coefficient (index of internal consistency reliability) ranged from 0.643 to 0.889 for the subscales. Evaluation of the validity of the Serbian version of NEI VFQ-25 is presented in the multi-trait-multi-method matrix and all items passed the convergent and discriminant validity tests. Rasch analysis showed a good measurement precision, but also demonstrated misfitting items and multidimensionality of the questionnaire.
  
  
  CONCLUSIONS
  Although traditional validation method indicates that the Serbian version of NEI VFQ-25 is a valid and reliable instrument for the assessment of vision specific QoL in Serbian populations aged 40 years or older, Rasch analysis revealed a substantial weakness of the questionnaire that should be taken into consideration when interpreting the results.
authors.affiliation: Clinic for Ophthalmology, Medical Faculty of Military Medical Academy, University of Defense, Belgrade, Serbia. bojankovac1978@yahoo.com.
authors.forename: Bojan
authors.initials: B
authors.lastname: Kovac
authors.affiliation: Clinic for Ophthalmology, Medical Faculty of Military Medical Academy, University of Defense, Belgrade, Serbia. vuki@eunet.rs.
authors.forename: Miroslav
authors.initials: M
authors.lastname: Vukosavljevic
authors.affiliation: Clinical Center of Serbia, Faculty of Medicine, University of Belgrade, Belgrade, Serbia. jelenadjokic2003@yahoo.co.uk.
authors.forename: Jelena
authors.initials: J
authors.lastname: Djokic Kovac
authors.affiliation: Clinic for Ophthalmology, Medical Faculty of Military Medical Academy, University of Defense, Belgrade, Serbia. resan.mirko@gmail.com.
authors.forename: Mirko
authors.initials: M
authors.lastname: Resan
authors.affiliation: Institute of Medical Statistics and Informatics, Faculty of Medicine, University of Belgrade, Belgrade, Serbia. gtrajkovic@gmail.com.
authors.forename: Goran
authors.initials: G
authors.lastname: Trajkovic
authors.affiliation: Institute of Social Medicine, Faculty of Medicine, University of Belgrade, Belgrade, Serbia. drjankojankovic@yahoo.com.
authors.forename: Janko
authors.initials: J
authors.lastname: Jankovic
authors.affiliation: Clinic for Ophthalmology, Medical Faculty of Military Medical Academy, University of Defense, Belgrade, Serbia. ciki1611@yahoo.com.
authors.forename: Milena
authors.initials: M
authors.lastname: Smiljanic
authors.affiliation: Institute of Epidemiology, Faculty of Medicine, University of Belgrade, Visegradska 26a, PO Box 20, 11129, Belgrade 102, Serbia. anita.grgurevic@gmail.com.
authors.forename: Anita
authors.initials: A
authors.lastname: Grgurevic
mesh_terms: D000328:Adult; D000368:Aged; D002908:Chronic Disease; D003431:Cross-Cultural Comparison; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011594:Psychometrics / Q000295:instrumentation / Q000379:methods; D011788:Quality of Life / Q000523:psychology*; D015203:Reproducibility of Results; D055771:Serbia; D011795:Surveys and Questionnaires / Q000592:standards*; D014786:Vision Disorders / Q000175:diagnosis* / Q000523:psychology*; D019987:Persons with Visual Disabilities / Q000706:statistics & numerical data*