Validation and reliability of the VF-14 questionnaire in a German population.
OBJECTIVE
To evaluate the validity, reliability, and measurement characteristics of the Visual Function 14 (VF-14) in a German sample using Rasch analysis.


METHODS
This was a clinic-based, cross-sectional study with 184 patients with low vision recruited from an outpatient clinic at a German eye hospital. Participants underwent a clinical examination and completed the German VF-14 scale. The validity of the VF-14 scale was assessed using Rasch analysis. The main outcome measure was the overall functional score provided by the VF-14.


RESULTS
After collapsing two response categories for items 13 and 14, the VF-14 scale satisfied fundamental criteria to achieve fit to the Rasch model, namely, ordered thresholds, the ability to distinguish between different strata of participant ability, absence of misfitting items, no evidence of unidimensionality, and no significant differential item functioning for key sociodemographic covariates. The VF-14 is able to discriminate between participants with different levels of vision impairment and across different cultural groups.


CONCLUSIONS
The VF-14 is a valid, reliable, and unidimensional questionnaire for use in a German population. These findings contribute to the growing evidence base for second generation patient reported outcome measures in ophthalmology, and support the use of the German VF-14 in tertiary eye clinics in Germany to capture the impact of visual impairment on visual function from the patient's perspective and to inform low vision rehabilitation and interventions.
Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, Melbourne, Australia.
Peggy Pei-Chia
PP
Chiang
Eva
E
Fenwick
Manjula
M
Marella
Robert
R
Finger
Ecosse
E
Lamoureux
D000368:Aged; D000369:Aged, 80 and over; D000554:Ambulatory Care Facilities / Q000592:standards; D003430:Cross-Sectional Studies; D003466:Cultural Characteristics; D005260:Female; D005858:Germany; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care / Q000379:methods; D011594:Psychometrics / Q000592:standards; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*; D015354:Vision, Low / Q000175:diagnosis* / Q000208:ethnology / Q000534:rehabilitation*