The fact of widespread public ignorance poses serious challenges to the theory of democratic government. Voters often not only don't understand the issues under public deliberation, often they don't know which politician or party is on what side of the issue.

At least some scholars have said that this issue driven view of public ignorance over-emphasizes issues, positions and ideas. Voters might be ignorant of those because they aren't very interested in them. There's some truth to this idea. Poltiical rhetoric, campaign promises and debating positions are poor predictors of actual political outcomes. Take, for example, President Barack Obama's promises to put every bill passed by Congress online for five days before he signed it into law. Well, so far Obama has signed two dozen bills and never once waited five days. Poltiical promises are not indicative of future performance.

Some hope for restoring faith in the effectiveness of democracy has come from the idea that while voters may not be all that big on ideas and words, they may be able to judge the competence of politicians.The idea is that they know enough to tell when incumbents are doing a good job by not screwing things up and throwing out those who are.

Unfortunately, effectively judging the competence of politicians requires citizens to be able to tell the difference between conditions caused by incumbents' policies and those that merely happened to occur on their watch without any such causal connections. In short, voters may be fooled by randomness into thinking that skillful politicians are improving things rather than simply enjoying lucky timing.

Tim Harford sums up recent scholarship on the matter (hat tip Ilya Somin):

The question is, can the voters tell the difference between an incompetent government and an unlucky one? Andrew Leigh, an economist at Australian National University, thinks not. In a recent article in the Oxford Bulletin of Economics and Statistics, he looks at 268 elections held across the world between 1978 and 1999. He estimates how much of a country’s economic performance is due to booms in the world economy and how much is due to competent government – and whether the voters can tell the difference.

Both matter, but as far as the voters are concerned, it is better to be a lucky government than a skilful one. For instance, a one-percentage point increase in world economic growth above the norm is associated with a hefty rise in the chance that incumbents will be re-elected – from the typical chance of 57 per cent to a more than decent 64 per cent. A stellar domestic performance, outpacing world growth by one percentage point, contributes less than half as much to the chances of being re-elected, raising them from 57 to 60 per cent.

Why are voters so wretchedly ungrateful? The common-sense answer is that it is not easy to distinguish a lucky government from a skilful one. In addition – and this point is less obvious – an individual voter has little incentive to do so. We all know that elections are almost never decided by a single vote, and so each voter would be right to conclude that her vote is highly unlikely to make a difference.

We vote for many reasons – a sense of duty, a desire to participate, and so on – but nobody votes under the illusion that it’s all down to him. And if the result does not depend on any particular one of us, trying to disentangle luck from skill by ploughing through the latest reports from the International Monetary Fund is likely to remain a minority hobby.

One other thing: Andrew Leigh finds some slight evidence that countries with high newspaper circulation have voters better able to distinguish luck from skill. Radio does not help, and television makes things worse. One more reason to switch off your set and pick up the Financial Times.