FairVote has posted this new report.  Here is a summary:

This report analyzes turnout data for the 146 primary runoff elections held between 1994 and 2010.  Primary runoffs are elections between the top two vote-getters that are held after the initial primary should no candidate surpass a certain vote threshold (typically a majority) in the first round. However, these elections are plagued with declining turnout that negates the representative nature of the system.  Noting the numerous factors that may impact turnout decline, this report attempts to quanify and measure these effects to promote the best possible election policy.