Validity of measured party positions on European integration: Assumptions, approaches, and a comparison of alternative measures

A variety of methodologies have been employed in order to measure the positions of political parties on the issue of European Integration. This paper compares four types of measures of party position: reputational, textual, behavioral, and self reported indicators. These indicators are assessed in terms of their content validity, convergent validity, and, construct validity. All of these approaches yield plausible measures which correlate reasonably well with each other, although care must be taken with the creation of indices from the Comparative Manifesto Project dataset. However, these indicators are not interchangeable, and the results of substantive research on EU politics are dependent, to an alarming extent, on the choice of indicators. Careful attention should be paid to the choice of measures, and the theoretical justification of any measure used. Future researchers would be well advised to test whether their results are robust across alternative measures of party positions.