The Dynamics of Issue Diversity in Party Rhetoric.

An important property of any party system is the range of issues it presents to the electorate. Party systems are often characterized in terms of the level of ideological polarization, but rarely in terms of the relative amount of issue choice afforded to voters; what we refer to as issue diversity. In this paper, we present an innovate approach to measuring issue diversity and we examine what explains variation in issue diversity over time. Following the issue competition literature, we would expect that parties emphasize different issues (issue divergence is the norm). This theoretical approach does not, however, explain why issue diversity changes over time. We present an alternative explanation that draws upon the dynamic representation model. We argue that issue diversity is primarily driven by public opinion, and that parties in government as well as opposition parties are driven by the same incentives to diversify (or narrow) their issue appeal. These propositions are tested by analyzing party leader speeches in two parliamentary systems, Britain and Denmark, in the period 1953-2007, using time series analysis. ..PAT.-Unpublished Manuscript [ABSTRACT FROM AUTHOR]