You know how sometimes, when it's really really hot, you get this urge to crank up the old spreadsheet, download a bunch of numbers from the Web and start crunching away like there's no next fiscal year?

Me neither. But I did spend a bit of the past week watching the Democratic National Convention on TV, and I needed something to exercise my mind while that was going on. Convention season is the one time every four years when we pretend that political parties matter. In general we have accepted the reality that campaigns for national office have become entrepreneurial, united more by shared political consultants than by old-fashioned parties.

Is there a difference between the parties that transcends the differences between the candidates? Is one of the parties, for example, a better steward of the economy? One year won't tell you much, or even one administration. But surely differences will emerge over half a century or so, if they exist. With that thought, I headed for the Web. Specifically, I went to the charts attached to the President's Economic Report, released in February. There I downloaded like a madman and then distilled the mess into a few key stats.

The figures I'm using are from the 43 years 1960 through 2002.This odd stretch of time reflects the years that are included in all of the charts I wanted to use. By doing it this way, I hope to convince you that I didn't choose the years to skew the results. Because the results are pretty interesting. Maybe presidents have little power over the economy. And we know that they must fight with Congress over the budget. Still, elections are based on the premise that whom you vote for does matter. So let's at least en- tertain that assumption for a few minutes.

It turns out that Democratic presidents have a much better record than Republicans. They win a head-to-head comparison in almost every category. Real growth averaged 4.09 percent in Democratic years, 2.75 percent in Republican years. Unemployment was 6.44 percent on average under Republican presidents and 5.33 percent under Democrats. The federal government spent more under Republicans than Democrats (20.87 percent of gross domestic product, compared with 19.58 percent), and that remains true even if you exclude defense (13.76 for the Democrats; 14.97 for the Republicans).

What else? Inflation was lower under Democratic presidents (3.81 percent on average, compared with 4.85 percent). And annual deficits took more than twice as much of GDP under Republicans as under Democrats (2.74 percent versus 1.21 percent). Republicans won by a nose on government revenue (i.e., taxes), taking 18.12 percent of GDP compared with 18.39 percent. That, of course, is why they lost on the size of the deficit. Personal income per capita was also a bit higher in Republican years ($16,061) than in Democratic ones ($15,565). But that is because more of the Republican years came later, when the country was more prosperous already.

There will be many objections to all this, some of them valid. For example, a president can't fairly be held responsible for the economy from the day he takes office. So let's give them all a year. That is, let's allocate each year of an administration to the party that controlled the White House the year before. Guess what. The numbers change, but the bottom-line tally is exactly the same: higher growth, lower unemployment, lower government spending, lower inflation and so on under the Democrats. Lower taxes under the Republicans.

But maybe we are taking too long a view. The Republican Party considers itself born again in 1981, when Ronald Reagan became president. That's when Republicans got serious about cutting taxes, reducing the size of government and making the country prosperous. Allegedly. But doing all the same calculations for the years 1982 through 2002, and giving each president's policies a year to take effect, changes only one result: The Democrats pull ahead of the Republicans on per capita personal income.

As they say in the brokerage ads, past results are no guarantee of future performance.

The writer is editorial and opinion editor of the Los Angeles Times.