TY - JOUR
T1 - Psychometric properties of visual functioning index using Rasch analysis
AU - Gothwal, Vijaya
AU - Wright, Thomas
AU - Lamoureux, Ecosse
AU - Pesudovs, Konrad
PY - 2010/11
Y1 - 2010/11
N2 - Purpose:- The visual functioning index (VFI) was one of the first questionnaires developed using classical test theory to assess outcomes of cataract surgery. However, it was not Rasch-validated. The objective of this study was to examine the psychometric properties of the VFI using Rasch analysis in patients with cataract. Methods:- The 11-item VFI was self-administered to 243 patients (mean age 73.9years) drawn from a cataract surgery waiting list. We examined the response category thresholds, item fit statistics, differential item functioning and unidimensionality for the VFI and its three subscales. Results:- Category thresholds were ordered. The person separation and reliability were low, indicating the poor discriminatory ability of the VFI. No items misfit but there was suboptimal targeting of item difficulty to patient ability. On the whole the items in the VFI were too easy for the sample. Only one item showed moderate differential item functioning. Conclusion:- The VFI does not meet the stringent requirements of the Rasch model. However adding more items to suit the more able patients with cataract as well as those awaiting second-eye cataract surgery could optimize the VFI.
AB - Purpose:- The visual functioning index (VFI) was one of the first questionnaires developed using classical test theory to assess outcomes of cataract surgery. However, it was not Rasch-validated. The objective of this study was to examine the psychometric properties of the VFI using Rasch analysis in patients with cataract. Methods:- The 11-item VFI was self-administered to 243 patients (mean age 73.9years) drawn from a cataract surgery waiting list. We examined the response category thresholds, item fit statistics, differential item functioning and unidimensionality for the VFI and its three subscales. Results:- Category thresholds were ordered. The person separation and reliability were low, indicating the poor discriminatory ability of the VFI. No items misfit but there was suboptimal targeting of item difficulty to patient ability. On the whole the items in the VFI were too easy for the sample. Only one item showed moderate differential item functioning. Conclusion:- The VFI does not meet the stringent requirements of the Rasch model. However adding more items to suit the more able patients with cataract as well as those awaiting second-eye cataract surgery could optimize the VFI.
KW - cataract
KW - cataract surgery
KW - classical test theory
KW - Rasch analysis
KW - visual functioning index
UR - http://www.scopus.com/inward/record.url?scp=78349285958&partnerID=8YFLogxK
U2 - 10.1111/j.1755-3768.2009.01562.x
DO - 10.1111/j.1755-3768.2009.01562.x
M3 - Article
VL - 88
SP - 797
EP - 803
JO - Acta Ophthalmologica Scandinavica
JF - Acta Ophthalmologica Scandinavica
SN - 1395-3907
IS - 7
ER -