Amorim Neto, Octavio; Lobo, Marina Costa (2009). "Portugal's semi-presidentialism (re)considered: An assessment of the president's role in the policy process, 1976–2006". European Journal of Political Research (dalam bahasa Inggeris). 48 (2): 234–255. doi:10.1111/j.1475-6765.2008.00833.x.