Julvez J, Forns M, Ribas-Fito N, Mazon C, Torrent M, Garcia-Esteban R, Ellison-Loschmann L, Sunyer J. Psychometric characteristics of the California Preschool Social Competence Scale in a spanish population sample. Early Educ Dev. 2008;19(5):795-815.
Michels KB, Rothman KJ. Update on unethical use of placebos in randomised trials. Bioethics. 2003 Apr;17(2):188-204.