Teles, A. G., Carreira, M., Alarcão, V., Aragüés, J. M., Lopes, L., Mascarenhas, M....Costa, J. G. (2008). Prevalence, severity, and risk factors for erectile dysfunction in a representative sample of 3,548 Portuguese men aged 40 to 69 years attending primary healthcare centers: results of the Portuguese erectile dysfunction study. Journal of Sexual Medicine. 5 (6), 1317-1324