Construct validation of the Amblyopia and Strabismus Questionnaire (A&SQ) by factor analysis

Abstract

Background The Amblyopia and Strabismus Questionnaire (A&SQ) was previously developed to assess quality of life (QoL) in amblyopia and/or strabismus patients. Here, factor analysis with Varimax rotation was employed to confirm that the questions of the A&SQ correlated to dimensions of quality of life (QoL) in such patients. Methods Responses on the A&SQ from three groups were analyzed: healthy adults (controls) (n = 53), amblyopia and/ or strabismus patients (n = 72), and a historic cohort of amblyopes born between 1962-1972 and occluded between 1968-1974 (n = 173). The correlations among the responses to the 26 A&SQ items were factor-analysed by Principal Component Analysis (PCA). As the development of the A&SQ was intuitive-deductive, it was expected that the pattern of correlation could be explained by the five a priori hypothesized dimensions: fear of losing the better eye, distance estimation, visual disorientation, diplopia, and social contact and cosmetic problems. Distribution of questions along the factors derived by PCA was examined by orthogonal Varimax rotation. Results Data from 296 respondents were analyzed. PCA provided that six factors (cutoff point eigenvalue >1.0) accumulatively explained 70.5% of the variance. All A&SQ dimensions but one matched with four factors found by Varimax rotation (factor loadings >0.50), while two factors pertained to the fifth dimension. The six factors explained 33.7% (social contact and cosmetic problems); 10.3% (near distance estimation); 8.7% (diplopia); 7.2% (visual disorientation); 6.3% (fear of losing the better eye); and 4.3% (far distance estimation), together 70.48% of the item variance. Conclusion The highly explained variance in the A&SQ scores by the factors found by the PCA confirmed the a priori hypothesized dimensions of this QoL instrument.

The Italian Version of the Amblyopia and Strabismus Questionnaire: Translation, Validation, and Reliability

“…Six factors (fear of losing the better eye, far distance estimation, near distance estimation, visual disorientation, diplopia, social contact and cosmetic problems) have been shown to underlie the structure of the US English version of the A&SQ. 10 Scaling assumptions were examined using the item discriminant validity approach, which is based on a comparison of the magnitude of the correlation of an item with its hypothesized scale as compared with other scales. 9 The multi-item multitrait correlation matrix is used to compare the correlation of an item with its hypothesized scale to the correlation of the same item with all other scales in the matrix.…”

The impact of strabismus on quality of life in adults with and without diplopia: a systematic review

“…They possess good internal consistency and construct validity, and are discriminatory and concurrent. 44,45 In an attempt to identify the effects of amblyopia separately from strabismus utilizing modern measurement theory, Vianya-Estopa et al 47 found that many of the strabismus subgroup items were not normally distributed and had significant skew, mainly as a result of high ceiling effects. In addition, a number of participants had difficulty with a large majority of the items and with some of the scale labels.…”

Health-related quality of life measures (HRQoL) in patients with amblyopia and strabismus: a systematic review

“…Validity has been reported in terms of discriminatory validity,7 concurrent validity7 and construct validity9 10 (see table 1). An English-language version has also been developed and has shown to be both reliable and valid 8…”