This week one of our site editors received an email from a junior PR person asking for the site’s ad rate. The reason for the email dawned on me only after a while: this publicist was determining the ad value equivalent of a recent PR campaign, one component of which was a successfully pitched story on our site.

Advertising value equivalency (or AVE) is one of those things I’d read about, and even written about a bit, but had never seen in the wild. I’m sure I’ve been complicit in many a PR scheme, though no publicist has ever asked me for my publication’s ad rate. The fact that it’s happening in 2010 is mindblowing. PR, after all, is on the way up. Among the constant reminders that we live in a media-made world are the facts that Britain’s new prime minister is a former PR executive and more and more corporate activity seems to be judged by the amount of PR — or earned media — it gets. That goes double for the corporate activity known as advertising.

So to try and develop a correlation between the two just seems strange, all the more so when you look under the hood of ad equivalency. How the metric is applied varies wildly, but it’s generally based on a simple concept: What would news coverage have cost if it were purchased as an ad buy of comparable space (or time.) For years, the metric’s had PR people measuring column space in newspaper clippings mentioning their clients, counting seconds of TV news broadcasts, and, now, guesstimating online impressions in an effort to determine a reach. That reach is then multiplied by ad rates plucked from media kits. It doesn’t matter for the sake of the exercise that in practice those rates get discounted in negotiation. As you can imagine, this kind of conjuring results in inflation that Zimbabwe would look at in awe.

It’s easy to see why this metric has long been used by the PR trade. Compared to the spendthrift practice and culture of advertising, a historically undisciplined discipline whose budgets are ballooned by the high-priced creative talent, pricey shoots, and expensive media buys, PR seems downright cheap. Yet in recent years any number of voices from within the industry have criticized AVE as an antiquated way of expressing value that’s built on a flimsy methodology. Common criticisms of AVE include: its ignorance of the coverage’s tone and impact; its spottiness in measuring the reach of coverage; its failure to account for the value of news kept out of the media. That’s just for starters. The only thing AVE can be counted on to do is tally up the volume of coverage, translating it into a big dollar figure that makes the enterprise of PR more meaningful to senior executives accustomed to big-ticket marketing projects.

“It is a highly suspect and yet strangely resilient metric,” says Julia Hood, Publishing Director of PRWeek and DM News (and my old boss).

That resilience is even more curious in light of the news culture on today’s internet. A PR person may pitch a news story to an online journalist or blogger in a fairly traditional manner, but there’s a whole afterlife of reader comments, and Facebooking and Tweeting, to say nothing of search-engine results pages where news stories are born again with every query inputted in Google. Part of my surprise that AVE was still around stemmed from the sheer impossibility of understanding how perception is changed online, let alone ascribing a dollar value to that change. How can you put a price tag on Tweet? How do you deduct for a vicious comment thread flaming your client’s brand? If nothing else, the rise of social media should be an opportunity to kill off the rotted old metric, once and for all. But that proposition begs a question: what will replace AVE?

Despite the social media-spawned complexity, new measurement ideas aren’t needed, Hood says. Many of the currently existing ones “are effective when they’re actually used. Consumer research before and after a campaign, the tracking of tonality and message delivery, and marketing mix modeling are all viable measurement techniques. The problem is these metrics tend to be costly and time consuming, and they don’t clearly or easily answer the basic question that marketers in particular want answered – how do these activities impact sales?”

That the PR industry is struggling to agree on a metric based on the ringing of registers, due in part to the lack of direct causality between the consumption of editorial and a purchase or some other action, leaves something of an opening for AVE, “because it’s a cheap, easy metric, and because it relates to a fundamental that everyone can understand, regardless of their PR acumen,” says Hood.

That “everyone” includes our junior PR person trying to determine our ad rates. In the end, we decided to help her defend her role and coughed up a CPM. It was, depending on how you look at these things, a little on the high side.

Matt Creamer is executive editor of Breaking Media. You can follow him on Twitter at @matt_creamer.