The Influence of Legislators' Endorsements in Party Leadership Elections

Abstract

In the 2010 election for the post of leader of the British Labour party, almost all members of parliament (MPs) endorsed one of five leadership candidates. I investigate the effect of these endorsements on the votes cast for candidates in each Westminster constituency. I find that an MP's endorsement caused an average increase of 7.5 percentage points in the vote share of the endorsed candidate in that MP's constituency.