Why is it only some People who Support Parties actually end up Joining Them? Evidence from Six British Political Parties

What makes people join a political party is probably the best-theorized and most commonly-studied topic in research on party members, with many of those who conducting it employing Seyd and Whitleley’s ‘General Incentives’, model which combines social-psychological and rational choice motivations to provide a persuasive answer to the puzzle. Empirically, as the recently-published comparative volume edited by van Haute and Gauja attests, there is widespread agreement that, at least in liberal democracies where patronage no longer plays such a big role, purposive, collective ideological incentives are much more important reasons for joining a party than are selective, material incentives – even if social norms and process incentives can also be important. Nearly all this research, however, is based on surveys of people who have actually joined parties, not on surveys of people who haven’t. This Paper combines surveys of original party members of the six biggest political parties in Britain with simultaneous surveys of people who, while they declare themselves strong supporters of those same parties, have not gone so far as to join them. When we put members and non-member partisans together, do existing explanations of why people join parties still hold good?