"My background is economics," says Greg Stuart, president of the Interactive Advertising Bureau, "and I don't understand it. The product goes down, the cost goes up." Stuart, who is responsible for promoting internet advertising as an alternative - or at least a supplement - to network TV advertising, was adding his voice to the many (including mine in this space last week) puzzled by the resilience of TV ads at a time when the quality of the product is lower than at any time in recent memory.Stuart was speaking at an industry gathering to discuss cross-media advertising. Representatives of newspapers, magazines, local TV, cable TV, outdoor, online, radio, and direct marketing were there to pile on to network TV, with PR conspicuously absent. (PR doesn't need to pay any of those folks to get its message out, which means media types can't make any money off it, which, in turn, means it doesn't rate a seat at this kind of table.) Another knock against TV advertising came from a recent survey by an advertising trade publication, which found that media advertising does the worst job of any marketing discipline in proving ROI and that network TV is the worst of all media. Network TV, which sold out its inventory ahead of the new season as it increased its rates significantly, was singled out as the worst medium at providing ROI by 32% of respondents, who included marketing managers and other senior corporate executives. Before we get too excited, however, it's important to note that PR was cited as the worst marketing discipline for proving ROI by 25% of respondents - better than TV advertising, but worse than all other disciplines, including direct mail and the internet. In discussions about PR measurement, I've always been puzzled by the assumption of many PR executives that TV advertising has been able to demonstrate its effectiveness in ways that PR has not. After all, there's nothing inherently more credible about advertising reach and frequency than there is about PR column inches. Now we have a study that seems to indicate that television advertising hasn't done a particularly good job of proving itself after all. A cynic might suggest that marketers buy TV ads not because they work - there's apparently little evidence that they do - but because everyone else does, or because that's the way it's always been done. But the reality is that the great brands of the past 20 years or so - Microsoft, Southwest Airlines, Starbucks, Amazon - have been built not by television ads, but by PR. We know PR can get the job done. We just need to find a way to prove it to skeptical marketers. Paul Holmes has spent the past 16 years writing about the PR business for publications including PRWeek, Inside PR, and Reputation Management. He is currently president of The Holmes Group and editor of www.holmesreport.com.