New York lottery ticket sales per capita in 2012, by zip code.

Jeremy Singer-Vine / BuzzFeed News

You may want to watch your wallet on days when your team is winning unexpectedly or the sun breaks surprisingly through the clouds. That’s all it took to increase lottery ticket sales in New York City, statisticians report in a new study.

The $1.6 billion Powerball jackpot announced last week adds to the interest in the $70 billion spent yearly on lottery tickets in 43 states across the U.S. American enthusiasm for lotteries, despite the astronomically bad chances of winning, has long baffled the mathematically minded.

“Unrealistic optimism certainly plays a role in buying lottery tickets,” New York University statistician Ross Otto, who headed the sunny day lottery study, told BuzzFeed News. “One suspicion is that people play the lottery when they are feeling good.”

The theory that Otto and colleagues examined in an upcoming Psychological Science journal study feeds into a long-running debate over why people gamble. Lottery ticket buyers might be depressed and buy tickets out of desperation, argues one side. Or they may be unduly cheerful about their chances of winning, and that might blind them to tough odds.

In a bid to examine the role that a good mood plays in fleecing gamblers, the study examined New York City sales of every daily, non-jackpot lottery game in Gotham in 2012, including “Numbers,” “Win4,” “Pick10,” ”Take5," and “QuickDraw." A typical one, Take5, offered 1-in-575,000 odds against winning a first prize and 1-in-10 odds of some kind of a small payout, basically another ticket. Looking for what might make gamblers happy or sad, the researchers compared those lottery ticket sales against the daily weather and the up-and-downs of New York’s local pro sports teams (such as the NFL’s New York Giants, who won the Super Bowl in 2012).

Otto’s team obtained the purchase information through a public records request to the New York Lottery (motto: “Hey, you never know”) run by the New York State Gaming Commission — an innovative strategy, given most researchers’ reliance on lab experiments. The lottery data covered $1.3 billion in daily ticket purchases across 174 zip codes in New York City. A quick look echoed previous lottery studies by confirming that people spent as much as 2% of their income on lottery tickets in poor neighborhoods, and much less of it in wealthy ones.

Kena Betancur / AFP / Getty Images

The new analysis detected a small but significant uptick in daily lottery sales on unexpectedly sunny days, or on days following big wins by the local teams. Together, the two factors appeared to account for an extra 1 out of every 200 tickets. People bought an extra $160,000 in tickets, city-wide, on days when multiple home teams won, the researchers estimate. The effect was similar across both rich and poor neighborhoods, which argued for a good mood effect in the sales.

The weather had a slightly stronger effect than the sports wins. One possible reason: “Everybody has to deal with the weather, not just sports fans,” Otto said.

Another striking finding: Sunshine seemed to boost lottery optimism only after cloudy days. It’s the unexpectedness of good fortune that seemed linked to more gambling, rather than a steady drumbeat of wins or nice days, psychologist Stefan Schulreich of Germany’s Freie Universität Berlin told BuzzFeed News.

Gambling treatment expert Alexander Blaszczynski of Australia’s University of Sydney, however, cautioned that other effects might explain the uptick in ticket sales seen in the study. People might simply spend more time outside their homes on a sunny day, or see more ads for the lottery during a sporting event.

“It’s a small, subtle effect, but it is in there,” Otto said. But he acknowledged that other explanations might also explain help sunny day upticks in lottery sales, and says that more studies in other cities are needed before psychologists would buy into his results.

“We are showing that optimism is irrational, after all, so we ought to be cautious,” he said.

Irrational optimism, of course, may be just what it takes to make someone a New Yorker. Lottery ticket sales data (below) from the study show people all over the city do like to bet on things going their way:

NYC Lottery Sales Per Capita, 2012

Note: The data represents lottery sales in each ZIP code divided by the number of adult residents in the ZIP code. In some ZIP codes — such as those around Times Square — many people who purchase lottery tickets do not reside there.

Map: BuzzFeed News / Data: Ross Otto