For weeks, Barack Obama's campaign has been trumpeting the fact that John McCain has agreed with President Bush 90 percent of the time.
There is a commercial that shows McCain himself saying: "The president and I agree on most issues. There was a recent study that showed I had voted with the president 90 percent of the time - higher than a lot of even my Republican colleagues."
In his acceptance speech at Denver's Invesco Field, Obama said: "McCain likes to talk about judgment, but really, what does it say about your judgment when you think George Bush has been right more than 90 percent of the time? I don't know about you, but I'm not ready to take a 10 percent chance on change."
It sounds self-explanatory, but what does it really means to support the administration 90 percent of the time?
The calculation comes from data provided by Congressional Quarterly, which compiles the roll-call votes on issues in which the president has taken a clear position. The votes span everything from war funding to renewal of the Patriot Act to judicial and cabinet nominations.
And, indeed, CQ reports that in these votes McCain has averaged 90 percent agreement with the president since 2001.
However, while not exactly a case of figures lie and liars figure, there is more to this story.
John Coleman, chairman of the political science department at the University of Wisconsin-Madison, has researched the 90 percent assertion and told me there are a few considerations the CQ data do not include. For instance, the president could take a position on a piece of legislation without actually doing much politically to see that it passes or fails. In those instances, the phrase voted with the president might overstate the president's political presence.
It's also important, Coleman said, to consider issues a president supports that never reach resolution. President Bill Clinton's attempts to change health care, for example, or Bush's Social Security initiatives - neither of which show up in the CQ data because Congress never acted on them.
Sometimes the final vote doesn't mirror what the administration intended. "A roll-call vote is the end of a process during which the president might have had to abandon major aspects of his policy in the days or months leading up to the vote. That means a senator or representative can be labeled as siding with the president because of the roll-call vote, even though in the buildup to the vote, he or she may have worked against things the president wanted included in or excluded from the vote," Coleman said.
There is also significant fluctuation by year. Consider that Sen. Joe Biden has agreed with the president 52 percent of the time since 2001. (And no, that's not a number front-loaded to the immediate aftermath of Sept. 11, 2001.) In 2004, Biden agreed with the president 77 percent of the time.
"So maybe that indicates that everyone's support level is at risk of being inflated by this measure," Coleman said. "Or we'd have to conclude that Biden was really that supportive of Bush, which seems dubious."
Coleman's theory would seem to apply to the president's party as well. Sen. Arlen Specter, often targeted by Republican conservatives for his centrism, actually has agreed with the president more than 82 percent of the time during the Bush years.
So what about Obama? In 2006, the last year he was present for at least 95 percent of the votes on issues in which Bush took a clear position, Obama voted with the president nearly half the time. (His total Bush presidential agreement tally is 40 percent.) That's truly a glass half empty or full situation. Also in 2006, Sen. Diane Feinstein joined the president 54 percent of the time; Biden, 55 percent; Chuck Schumer, 52 percent; Hillary Clinton, 50 percent. Harry Reid? 57 percent.
Here's another twist. According to WashingtonPost.com, since 2000, McCain has voted with a majority of his fellow Senate Republicans an average of 82 percent of the time. That's only slightly less than the average for all Republican senators, who toed the party line almost 87 percent of the time in the same period.
Meanwhile, Obama voted with a majority of Senate Democrats more than 95 percent of the time in both of his congressional sessions, while the average for Democratic senators was 87 percent.
Perhaps that figure supplies the McCain campaign with the data for its proposition that Obama's candidacy is less about change and more about the status quo.
Coleman said that to assess McCain's level of support for Bush at 90 percent is misleading "if you consider McCain's tendency to defect from the Republican Party line more frequently than the average Republican and consider his signature disagreements with Bush on some major policy goals, proposals, and administration of policy - like troop strategy in Iraq."
Also keep in mind that even the other party's candidates supported the president 40 percent to 52 percent of the time during the Bush years, Coleman said.
"Ultimately, I think you have to interpret the number in light of the other numbers to get a feel for its meaning," Coleman said. "Ninety percent sounds like a lot, but it may not seem like quite so much in light of other numbers."
Of course, Coleman added, McCain probably didn't do himself any favors by using the figure of 90 percent in agreement with Bush as a point of pride.