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E. S. Van de Graaf, G. W. van der Sterre, J. Passchier, H. van Kempen-du Saar, C. W. N. Looman, J. Felius, H. J. Simonsz; Factor Analysis With Varimax Rotation Confirms the Construct Validity of the Amblyopia and Strabismus Questionnaire. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2578.
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© ARVO (1962-2015); The Authors (2016-present)
The Amblyopia and Strabismus Questionnaire (A&SQ) was previously developed to assess quality of life in amblyopia and/or strabismus patients. Factor analysis, preliminarily reported at ARVO 2005, was now repeated with Varimax rotation to verify that the questions of the A&SQ correlated in an ordered manner to all components of quality of life of such patients.
Responses on the A&SQ from 3 groups were analyzed: healthy controls (n=53), amblyopia and strabismus patients (n=72) and a historic cohort of amblyopes who were born between 1962-1972 and occluded between 1968-1974 (n=173). The correlations among the responses on the 26 A&SQ questions within the 5 domains: fear of losing the better eye, problems with distance estimation, visual disorientation, diplopia and social contact & cosmetic problems were examined by Principal Component Analysis on the correlationmatrix (PCA). Distribution of questions along the factors derived by PCA was examined by orthogonal Varimax rotation.
Data from 296 respondents were analyzed. PCA provided that 6 factors (cutoff point eigenvalue >1.0) accumulatively explained 70.5% of the variance. Orthogonal Varimax rotation provided that 4 out of the 5 domains of the A&SQ showed an unidimensional separation on 4 factors (factor loadings >0.50), i.e. the questions within these domains did not require a rearrangement. In the one multidimensional domain: distance estimation, the questions pertaining to near distance estimation separated on the one remaining factor whereas the questions relating to far distance estimation separated on the other. The 6 factors explained 33.7% (soc contact & cosm), 10.3% (dist est at near), 8.7% (dipl); 7.2%(vis disor); 6.3% (fear loosing better eye) and 4.3% (dist est at dist) respectively of the response variance.
The very high explained variance in the A&SQ scores and the factors found by the PCA confirmed the a priori hypothesized dimensions of this HRQOL instrument.
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