The Definition of an Ad Impression

February 18, 2014

By Reid Tatoris, MediaPost

The most common unit of measurement in digital advertising is the impression. And, it’s the most common way that digital advertising is bought and sold today. It’s so commonplace that most people take for granted that they know what it means. Well, most people are wrong.

Most of us think that an impression means that an ad was shown to a consumer. They may not look at it, but they have the chance to see it, right?

Unfortunately, that’s wrong. An impression means one and only one thing. It means that an ad server was called. The official IAB definition reads: “‘Impression’ is a measurement of responses from a Web server to a page request from the user browser.”

Technically, here’s what happens: whatever ad server you use provides a “pixel” — a tiny, usually invisible image — that lives on each publisher page. When this image loads, the ad server is notified, and you get an impression. But an impression does not equal an ad opportunity. Three things get in the way:

Broken default: The ad is broken. No foul play here, just means that the wrong ad loaded, or something technical went wrong and the ad didn’t appear. Most ad networks will report, and try and manage, these numbers but it happens about 15% of the time.

Bot traffic: Hackers write bots, automated computer programs, to crawl the web for various reasons, like posting spam and creating phony accounts. These bots count as site views, falsely driving up the impression count of your ad. An ad server is called even though no human is on the site. Multiple studies show that up to 60% of all traffic on the web is bots.

Straight-up fraud: There is lots of money to be made in purposefully creating fraudulent impressions to steal ad dollars. Recently, a fake web trafficker came clean on the gory details. People will hide ads behind other ads, spoof their domain to trick ad networks into serving higher-paying ads on their site, and purposefully send bots to a site to drive up impressions.  Wenda Millard, president of MediaLink, claims that 25% of the entire online ad market is fraudulent. The end result is lots of traffic and lots of inaccurate measurement.

Most ad networks do want to control this, but with hundreds of thousands of sites involved, it’s impossible to police everyone. What you’re left with are some staggering numbers.

We start with the notion that only 15% of impressions ever have the possibility to be seen by a real person. Then, factor in that 54% of ads are not viewable (and we already discussed how flawed that metric is), and you’re left with only 8% of impressions that have the opportunity to be seen by a real person. Let me clarify: that does not mean that 8% of impressions are seen. That means only 8% have the chance to be seen. That’s an unbelievable amount of waste in an industry where metrics are a major selling point.

This begs the question, why do we pay so much attention to a metric that isn’t meaningful? In part, it’s because impressions are a very easy metric to measure, even if the information they provide ultimately isn't that useful. Furthermore, we've been measuring impressions for years, and that inertia is hard to overcome. But as a smart guy once told us: “Not everything that counts can be counted, and not everything that can be counted counts.” — Albert Einstein.

Let’s start trying to count what actually matters. What we really want to know is: was a brand message actually seen by a real live person? Measuring impressions, however easy it may be to do, doesn't answer this question. Measuring engagement does. As a first step, we should only count impressions that we know aren't fraudulent, and that we know aren't bot traffic. But to do even better, we should aim beyond impressions, to metrics that can tell us not only that a person saw an ad, but that they actually interacted with it.

There's no question that this will be more difficult than the old way of simply counting impressions and calling it a day. But if we push towards measuring what actually matters, we'll make everyone — advertisers, publishers, and consumers, too — happier.


"The Definition of an Ad Impression." Reid Tatoris. MediaPost, 02/18/14.

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