In the Washington Post, Shankar Vedantam writes about the “attraction effect”:
bq. Political pundits often argue that when two candidates share an interest in an issue, they hurt each other because they are competing for the same voters. This is partly true, but it ignores the fact that having multiple candidates interested in an issue increases the weight that voters attach to that issue at the expense of others. An increased focus on one issue can help all the candidates who are strong on that issue. You can see why researchers dub this phenomenon “the attraction effect” — candidates inadvertently help other candidates with similar views.
An implication for the 2008 Republican race:
bq. Mike Huckabee’s win in Iowa and his strong showing among social conservatives in other states, for example, may have helped Mitt Romney defeat Sen. John McCain (Ariz.) in Michigan and Nevada because Huckabee’s win raises the weight that voters attach to social conservatism. Huckabee is stronger than Romney on that issue, but a greater weight on social conservatism helps Romney because he is stronger on that issue than McCain — and because many Republicans prefer Romney to Huckabee on other issues.
This is an interesting and counterintuitive way to think about this race. Shankar cites a study by Diane Lowenthal. Another demonstration within the academic literature, with campaigns as its focus, is here (gated).
[Hat tip to Scott Adler.]