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³⁹ It has to be noted that this formula does not constitute the basis for the calculation of the policy positions of Europarties; it simply summarizes our theoretical model, according to which the policy position of a Europarty P_EUR can be explained by the policy preferences of its J national member parties P_NATj weighted by their legislative resources α_j. The policy positions of Europarties are measured independently on the basis of a content analysis of their election manifestos, as outlined in detail in the next section.

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⁵⁵ More precisely, the question is worded as follows: ‘Some say European unification should be pushed further. Others say it has already gone too far. What is your opinion? Please indicate your views using a 10-point-scale. On this scale, 1 means unification ‘has already gone too far’ and 10 means it ‘should be pushed further’. What number on this scale best describes your position?’.

⁵⁶ One could argue that party proximity could also be a good measure to identify the potential electorate. However, the same citizen can be close to different parties, so it is therefore not clear how multiple party identifications affect vote choice. At the same time, the level of response is lower, thus decreasing the number of respondents, especially for small parties.

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⁶⁶ Potentially, it is also possible that there is a reciprocal relationship between policy positions of Europarties and those of national parties. In addition to the suggested bottom-up relationship in which national parties influence policy position choice of Europarties, one could also advocate a top-down relationship in which Europarties could shape position formation of their national party members. We therefore conducted a Granger causality test in order to shed light on the direction of the relationship. This test indicated that the Europarties’ policy positions do not ‘Granger-cause’ the national parties’ policy positions (F = 0.104, Prob > F = 0.747). Conversely, national parties’ policy positions do ‘Granger-cause’ Europarties’ policy positions (F = 17.26, Prob > F = 0.000).

⁶⁷ To further test the robustness of the results, we also estimated OLS regression models with fixed effects for elections and Europarties to control for election-specific and Europarty-specifc explanatory factors. These additional model specifications similarly confirmed our findings. In addition, we also tested whether preference formation in the run-up to the 2004 EP election followed a different pattern due to the Eastern enlargement by including a fixed effect for the 2004 election. The analysis indicated that there is no systematic difference between the 2004 election and previous elections with regard to policy position choice within Europarties.

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