Putting parties in their place: Inferring party left-right ideological positions from party manifestos data

The left-right ideological positions of political parties play a central role in theorizing about many different aspects of democratic processes. Unfortunately, scholars are hindered in their ability to test existing theories by the limited availability of data that is comparable over time and across countries. This paper describes a simple 'vanilla' method for using manifestos data to estimate party left-right positions. It then tests this method and four existing ones by regressing a variety of accepted survey-based measures of left-right party positions on the estimates of party positions generated by the various techniques. Finally, analysis of the residuals from these regressions identifies the extent to which there are systematic sources of errors in using manifestos data to estimate party left-right positions. The vanilla method consistently produces the best estimates of party positions, and these estimates are quite good (less than one point, on average, from the estimates of other accepted approaches). Manifestos data, however, tend to locate extreme parties closer to the ideological center than do other survey-based approaches.