ANYONE who follows an election campaign too closely will sometimes get the feeling that politicians think voters are idiots. A new book says they are. Or rather, Bryan Caplan, an economics professor at George Mason University, makes the slightly politer claim that voters systematically favour irrational policies. In a democracy, rational politicians give them what they (irrationally) want. In “The Myth of the Rational Voter”, Mr Caplan explains why this happens, why it matters and what we can do about it.