In a new article entitled “Whose bread I don’t eat, his song I don’t sing? MPs’ outside earnings and dissenting voting behaviour”, recently published in the journal Party Politics, Philipp Mai deals with the question of whether politicians’ outside earnings affect their legislative behaviour, precisely their propensity to vote against the party line.
Voting against the party line is a rare phenomenon in most parliamentary democracies and not without risk for Members of Parliament (MPs). Although its determinants, i.e. which MP- or vote-related characteristics facilitate or impede vote defections, are a rather well studied topic in legislative studies, the role of moonlighting therein has never been thoroughly theorized nor empirically examined yet. Philipp argues that MPs with high outside earnings have a higher degree of financial and career-related independence from their party. Therefore, they can be less effectively disciplined by their parliamentary party group and, all else being equal, are expected to have a higher probability to vote against the party line than their non-moonlighting colleagues.
Empirically, he collected data for all MPs of the 18th parliamentary term of the German Bundestag (2013-2017) and tested his proposition quantitatively using logistic panel regressions against more than 115,000 individual voting decisions. The data support his hypothesis that MPs obtaining the bulk of their earnings outside parliament vote more often against the will of their party group leadership than those who do not have additional income besides their parliamentary mandate.
The findings of the paper have many implications for our understanding of how politicians’ career paths are linked to their political behaviour.