C. Spielberger, G. Buela-Casal, D. Agudelo, H. Carretero-Dios, and F. Santolaya, “Analysis of convergent and discriminant validity of the Spanish experimental version of the State-Trait Depression Questionnaire (ST-DEP)”, Actas Esp Psiquiatr, vol. 33, no. 6, pp. 374–382, Nov. 2005.