A. R. Freire and A. M. Belchior,  "Ideological Representation in Portugal: MPs-Electors Linkages in Terms of Left-Right Placement and Substantive Meaning", in Political Representation in Portugal: The Years of the Socialist Majority, 2005-2009, Freire, André & José Manuel Leite Viegas , Ed., Leya, E-book, 2015