Your vote can make a difference on Nov. 2 but the chances of it are far lower than those of being struck by lightning sometime within the next year.

Just ask Andrew Gelman, who teaches statistics and political science at Columbia University, and who co-authored a study published this year in Economic Inquiry showing the probability of a single vote proving decisive in a presidential election. (Answer: one in 10 million for voters in a handful of key swing states, and one in 60 million for the broad U.S. population.) Asked for the odds of a single voter deciding a race on Tuesday, Gelman offered an example using the House of Representatives.

Assume there are 200,000 voters in a district (out of about 750,000 who are eligible to vote), and assume the race is fairly close with the winner separated from the loser by no more than 10 percentage points. The odds of a single vote proving decisive are "on the order of one in 40,000," says Gelman. The probability of the district in question deciding which party controls the House, meanwhile, is "maybe one in 50." Multiply the two and the result is one in two million the approximate chance of a single vote deciding House control.

Lightning accidents have somehow become the benchmark for comparing the probability of unlikely events, but they're common enough that a support group exists for survivors: Lightning Strike & Electric Shock Survivors International

Of course, eligible voters should vote, regardless of the slim odds of their votes mattering. The system depends on it. Besides, voter turnout in America is already abysmally low, right?

Maybe not. Turnout improved sharply in the 2008 presidential election, and according to Michael McDonald, a George Mason University professor and senior fellow at the Brookings Institution, it has been measured wrong all along. Many alarmist reports of low voter participation have used math based on the voting-age population, which includes growing groups of people who are ineligible to vote, like non-citizens and felons. (All but two states, Maine and Vermont, restrict felon voting.) Based on the population of eligible voters only, the turnout rate in 2008 was about as high as it was in 1972.

It should surely be prodded even higher. There are plenty of proposals on how to do that: voting holidays, online polling, financial rewards, neighborhood canvassing and so on. However, researchers at Yale and the University of Northern Iowa have come up with a compellingly cheap plan involving pride and shame.

In a study published in the February 2008 issue of American Political Science Review, the authors presented the results of four different messages mailed to tens of thousands of voters in the August 2006 Michigan primaries. The baseline turnout rate was 29.7%. The first message read simply, Do Your Civic Duty--Vote!" It increased turnout by 1.8 percentage points. The second: "You Are Being Studied!" It added 2.5 percentage points to the baseline turnout. The third mailing listed whether the recipient had voted in previous elections, and explained that "we intend to mail an updated chart" after the upcoming primary. (Researchers can determine who voted and in some states which party they belong to, but not who they voted for.) This raised turnout by 4.8 percentage points.

Finally, a fourth mailing listed not only the past voting participation of the recipient, but that of their neighbors, as well. Turnout jumped 8.1 percentage points.

In a follow-up study published this year in Political Behavior, the researchers further dissected the numbers to show that pride-inducing mailings to past voters increase turnout, but not nearly as much as finger-wagging ones sent to non-voters. (We know who you are, and we ll see you on Tuesday.)