This morning, NBC’s First Read published their most recent list of the most hotly contested markets and found that Virginia, North Carolina, Colorado, and Florida only contributed one of the top-ten markets. For much of the summer, Virginia dominated the top-markets lists with Norfolk, Richmond, and Roanoke routinely vying for the top spot. Instead, nine of the top ten markets came from the midwestern battlegrounds and Nevada, where the polls have generally shown Obama performing better than the southeastern battlegrounds and Colorado.

So what does the shift in ad spending mean? Does it suggest that the campaigns believe Romney is likely to win Virginia, North Carolina, Florida, and Colorado and the race is now turning to Democratic-leaning turf? That’s one argument and it could have validity—especially in Florida and North Carolina. Perhaps the campaigns have assessed that Romney is likelier to win Virginia and Colorado than not, despite tight poll numbers. If true, then Romney is now on the offensive in the once Obama-leaning states searching for the final electoral votes, since wins in Virginia, North Carolina, Florida, and Colorado would get him to 257 electoral votes.

But the problem with using ad spending to glean too many insights into the campaign is that the numbers can almost always be reinterpreted with equal validity in the exact opposite direction. Imagine, for instance, that Obama is up by only a modest 3 points in the Obama-tilting states worth 281 electoral votes—Wisconsin, Ohio, New Hampshire, Iowa, and Nevada—while the race remained truly deadlocked in Virginia, Florida, and Colorado. In case anyone has lost track, there are 19 days until the election, so the Romney campaign needs to move the numbers in at least a few of those states very quickly, making increased ad spending imperative. The Obama campaign would understandably match their spending as best they could, especially since Team Romney appears to have an overall ad spending advantage that would allow Team Romney to outspend Obama by a decided margin in the Obama-tilting states like Ohio or Iowa if the Obama campaign didn't concentrate spending in those battlegrounds.

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There is one thing that can be fairly inferred from the ad numbers, as well as the polls: Obama is doing better in states like Ohio, Iowa, Nevada, and Wisconsin, while Romney is doing better in Florida, Virginia, and North Carolina. But "better" is a relative term, not a judgment on the absolute state of these races. The ad data can't resolve whether "relatively better" means that Obama is up 4 in Ohio but tied in Virginia or if Romney leads by 3 in Virginia and is down just one point in Ohio. Ultimately, that's the more important question.