Warttig SL, Forshaw MJ, South J, White AK. New, normative, English-sample data for the Short Form Perceived Stress Scale (PSS-4). J Health Psychol. 2013 Dec;18(12):1617-28. doi: 10.1177/1359105313508346
Garcia-Esteve L, Torres A, Navarro P, Aguado J, Ascaso C. Maternidad the planned y psicomorbilidad: un riesgo evitable / Unplanned pregnancy and psychological morbidity: an avoidable risk. Fac Med Barc. 2005 Jul;32(3):111-8.