Still Connected? The Attitudinal Representativeness of German Party Memberships

In modern representative democracies political parties are the main institutions responsible for providing linkage between citizens and the state. One way to do this is through organizational linkage mechanisms, especially the representation of a party’s voters through their membership. This paper tries to assess the attitudinal representativeness of German party memberships in terms of left-right positions using data from two party membership studies from 1998 and 2009. For information on the parties’ voters we resort to two accompanying population surveys. Initially, the extent of attitudinal representativeness is described using three indicators drawn from research on congruence: the mean difference between voters and party members, the standardized mean difference, and the “common area under the curve”. In a second step, the determinants of divergent attitudes of party members from the mean position of the parties’ voters are analyzed on an individual level, testing four possible explanations for this: the socio-demographic composition hypothesis, the organizational status hypothesis – better known as May’s law of curvilinear disparity –, the ideological motivation hypothesis as well as the party characteristics hypothesis. While party members tend to be ideologically more pronounced than their respective electoral base, the result shows that the attitudinal representativeness of nearly all parties has improved considerably from 1998 to 2009. The German party members are a fairly good representation of the left-right positions of the population at large. Testing the four hypotheses, it is revealed that the socio-demographic composition of most parties is indeed a problem for attitudinal representativeness: The socio-demographic groups underrepresented in party memberships tend to hold left-right positions diverging from their parties’ voters. Besides that, an individual ideological motivation leads to a further diversion from their electoral base. Finally, members of ideological parties tend to be closer to the position of their voters than the ones of catch-all parties.