One answer is to be precise and accurate in describing their sources of data. For example, Kantar statistics are estimates rather than exact totals, a difference that should be reflected in descriptions of them. There is also an important distinction between ad reservations and ads that have already aired, and this should be noted rather than simply referring to “TV ad spending.”

A second takeaway is that ad spending takes place in a volatile marketplace, in which rates rapidly change, many ads can be preempted and then must be refunded, and candidates and outside groups pull ads on short notice as they reallocate resources. Robin Kolodny, a political science professor at Temple University who studies campaign advertising, said a precise picture of TV ad spending will not emerge until early December when broadcasters disclose invoices that, unlike order forms, provide the costs and details of which political ads actually aired. “It’s much easier to do it after the fact then it is in real time,” Kolodny said. “That’s the real lesson.”

Finally, there is far more to be learned about campaign ad spending than simply overall expenditure totals. Unlike SMG Delta or the FEC, Kantar provides spot counts, which The New York Times yesterday described as a better measure of the ad wars than spending because it reflects an organization’s reach rather than the disparate prices that campaigns and outside groups pay for airtime. Kantar also offers a breakdown of the content of ads, which provides insight into campaign strategy and messaging. “Advertising isn’t just about the money,” said Wilner of Kantar’s campaign analysis team.

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Sasha Chavkin covers political money and influence for CJR's United States Project, our politics and policy desk. He has written for ProPublica, the Center for Public Integrity, and The New York World. Follow him on Twitter @sashachavkin.