The reliability and validity of the iterative expert survey approach for measuring parties' policy positions

A major innovation of the EUvox voting advice application that was made available for the 2014 elections to the European Parliament was that parties' policy positions were estimated using an iterative expert survey using what is known as the Delphi method. In this paper we briefly present this approach in comparison with other methods of estimating parties' positions, both in voting advice applications and more generally (expert surveys, content analysis of manifestos), and discuss the challenges of applying it in a cross-national setting. Drawing from the EUvox dataset that includes the positions of over 230 political parties across the EU, we examine the coding reliability, as well as the content, criterion, and construct validity of the method, and discuss the implications for comparative research.