The results of a quantitative investigation into the factors affecting coalition government membership in West European parliamentary democracies are reported in this article. Using a new data set covering the post-war era to 1990, separate logistic regression analyses are performed to determine what influences the odds of becoming the government ‘formateur’ and the odds of becoming a coalition partner. In addition, Laver and Shepsle's portfolio allocation theory is subjected to testing. Among the independent variables considered are a party's size, its previous experience in government, its willingness to trade off policy for office, and its ideological position in the parliamentary party system. The findings point to the important roles played by the formateur's preferences and by the need to build workable coalitions, given party-system constraints. They also suggest several criteria that ought to, but often do not, guide formal theory-building.
Paul Warwick (1996) studied this question.