van de Graaf, E. S., Felius, J., van Kempen-du Saar, H., Looman, C. W. N., Passchier, J., Kelderman, H., & Simonsz, H. J. (2009). Construct validation of the Amblyopia and Strabismus Questionnaire (A&SQ) by factor analysis. Springer-Verlag.

van de Graaf, Elizabeth S., Joost Felius, Hanneke van Kempen-du Saar, Casper W. N. Looman, Jan Passchier, Henk Kelderman, và Huibert J. Simonsz. Construct Validation of the Amblyopia and Strabismus Questionnaire (A&SQ) By Factor Analysis. Springer-Verlag, 2009.

van de Graaf, Elizabeth S., et al. Construct Validation of the Amblyopia and Strabismus Questionnaire (A&SQ) By Factor Analysis. Springer-Verlag, 2009.