According to The New York Times, the growth of online advertising is being stunted because nobody can get the basic visitor counts straight.
There’s also no one source for credible stats. Bloggers often turn to Technorati, but their data appears to be suspect, just like their competitors’ data. There’s Quantcast, but one needs to embed their code for it to return accurate data.
The marketing and ad blog universe–which expands exponentially by the day–now has its own tracking mechanism called the Power 150. Ad Age believes in it, but I’m not sure everyone else does.
Bottom line, traffic is but one imperfect measurement to consider when looking to place online ad units. How much influence a site has is not going to determined merely by looking at page views or unique visitors. Advertisers also need to know who is coming to a site, how long they spend there and what value they ultimately take away.