For Germany, Windolf/Haas (1989), Lorenz/Wagner (1991), Fitzenberger et al. (1999) and Beck/Fitzenberger (2004) all found that Social-Democrat (SPD) voters have a higher probability of being union members which is not surprising given the historically close relationship between the SPD and the labour movement.
exploredata-ZA2140_VarV3 exploredata-ZA2140_VarV61 exploredata-ZA2140_VarV422 exploredata-ZA2140_VarV401