Last year, the country ran controlled experiments in 435 different places, putting a number of candidates up against one another and tracking how much each raised and spent. By combining data from the Center for Reponsive Politics (the people behind campaign money site Open Secrets) and the actual 2012 results, we're able to get a sense for how money and vote totals correlate.

More money was spent on votes in closer races.

First, we took a look at how the margin of victory in each race (the raw vote total separating winner from loser) correlated to the cost-per-vote. That figure is how much each winning member of Congress spent divided by how many votes he or she got. If a candidate spent $100 campaigning and got 20 votes, each vote cost $5. (On average, the 435 winners spent $9.84 per vote.)

Below, the relationship between votes and vote-cost. Each blue dot is one winning campaign. The vertical axis is the number of votes in the margin of victory; horizatonal, cost per vote. At the top left, Rep. Chaka Fattah of Pennsylvania's 2nd district, who won by a heavy margin at a low cost. At bottom right, Minnesota's 6th, home of Rep. Michele Bachmann, who won by a small margin at a high cost. The red dotted line is the most important part of the graph. It shows the trend in all of the data. (This graph, unlike the others, uses a logarithmic scale on the x-axis.)

Notice that the red line drops sharply down to the right. In other words, as races grew tighter (few votes in the margin of victory), each vote grew more expensive. More important votes cost more.

The more you outspent your opponents, the more you won by.

More interesting is a look at how the size of the winning candidate's victory corresponds to how much more that person spent. (The first three graphs in this post correspond to spending, not what was raised by the campaign.) Here are all of the races, with the vertical axis showing the point spread of the victory (e.g., a 60 percent to 40 percent win is a 20 percentage point spread). The horizontal axis shows the percentage more or less that the winning candidate spent.

This, too, looks the way we'd expect. The greater the difference between how much the winner outspent his or her opponent, the more of a spread in the end result. The red line goes from lower left to upper right showing that trend.

But notice all of the dots at the far right. That's largely heavy incumbents, who won against opponents that weren't well-funded (like Rep. Fattah). What if we filter them out?

In close races, that effect was heightened.

If we only look at races that ended up within a 20-point spread — not close races at that margin, but not completely lopsided — the pattern shifts.

The most significant thing on this graph is the slope of that red line. It moves up and to the right much more steeply than for the chart above, showing all races. In other words, there's more of a correlation between spending differential and vote differential. This supports the idea that in closer races, money makes more of a difference.