Lots of publishers I have spoken to get a little confused when their ad impression count differs from their page impressions. So my goal here is to try to identify the common reasons for the differences. The fact that advertising systems count ads, not pages, is the first key difference.
The other day, I wrote what I thought was a handy guide to the basic web measurement concepts of page impressions, visits and unique user metrics. Haven’t read it? Please do so before reading this one.
Back? This time, I’m going to talk about a new impression metric that is often confused with the measurements I spoke about last time: the ad impression. To those of us in the digital advertising tech business, the ad impression is our measure of a website’s scale and value. However, our measurement counts advertisements, not most of the other things I talked about last time.
How do they differ then?
Last time, I noted that a page impression was counted every time someone viewed a web page. That page, however, may have three or four (and often many more) advertisements. Our industry, therefore, counts how many times advertisements are shown. So, one page impression may be one ad impression, but it may also be three ad impressions depending on the number of advertisement spaces a publisher has built into their pages. It’s important not to confuse them, as these impressions are very different.
Lots of publishers I have spoken to get a little confused when their ad impression count differs from their page impressions. So my goal here is to try to identify the common reasons for the differences. The fact that advertising systems count ads, not pages, is the first key difference.
Secondly, the advertising system will only count an advertisement impression when the browser requests the ad. It is not inconceivable that the ad system may not receive the ad request and therefore not count it (if the ad system is broken or slow, the user may not wait around for the ad). Result: the page impression is counted, but not the ad impression(s).
Thirdly, advertising systems try not to count robots, spiders and other automated web systems that make the web work for us but do not represent a human actually looking at an advertisement. After all, a computer is not really in a position to buy a new car. I noted last time that when counting page impressions, those things should not be counted either. However, if the system measuring your pages is configured with a different list of what is – and what is not – a web robot, then some pages may be counted when the advertising system might not count – or vice versa. Ideally, vendors of both systems would use the same list, but sometimes, for many different reasons, they can’t. So the result is that a page-counting system may not quite be counting the same people as an advertising system. The main thing here is that this is OK. The systems have different counts because they look at different things. You know, sometimes there are apples and sometimes oranges.
The next reason for the difference is simply due to the way websites are set up. Many sites do not put advertisements on every page of their site. It may sound obvious, but if there is no advertisement placed on the page, it’s never going to count as an ad impression. I once spent a day trawling through the data for a very large, well-staffed, UK website to help explain differences in page and ad impression counts, and I discovered hundreds of pages that contained no ads. The site had sprawled, and their site management systems were simply not inserting all the right codes. The clever coders and designers who build websites sometimes miss this. There’s a whole other post about how, if your site is ad-funded, advertising should be part of the design process – but I digress.
Ask your web development team to look at all the places on your site where there are advertisements that don’t call the ad server to deliver them. This is often referred to as ‘hard-coding’ because the advertisement code is hard-wired directly into the web page rather than being designed to request an ad from the ad server. This is a very common cause of differences between website page counts and ad impression counts. It’s often done because the ‘hard-wired’ ad will remain for a long time, and the publisher does not want to pay the ad-serving company to continually select the exact same advertising copy in the exact same space. But as with our examples above, if the ad server isn’t asked to select the advertisement, it can’t do its job or count it.
It’s worth pointing out that sometimes the ad server appears to be serving lots of advertisements, and even when accounting for multiple ads on a single page, the number still looks too high. Here, it’s worth checking that the ad-server code is correct on the page. Because ad-server code tries to do clever things to account for the many ways people view your site (across multiple browsers that support different standards), incorrectly formatted code may request multiple advertisements when only one is displayed. The result is too high counts because the ad server is unable to determine exactly which one will be displayed, so it assumes they are all valid. This is one for your coding team.
Also in the ‘too many ads counted’ category is the fact that you must be comparing the same site boundaries. Is your ad technology serving advertisements elsewhere? If it is, we must ask whether the code in those ‘other’ places is correct or is telling the ad-server that the request is coming from somewhere else. Most ad servers rely on the code on the page, the ad request, to know where the ad is being delivered. If your request tells the system to select an advertisement for Site A, but it is, in reality, Site B, then the ad system may assign the count to the wrong site (worse, it may also select an advertisement that is not valid for Site B). Is the right code in the right place?
Finally, there are a couple of other reasons that add to the differences. Some people actively block advertisements using special software in their browser. If they do, then the advertising system won’t count them. Some ad systems also try to track suspicious behaviour (such as people clicking on advertisements many times, inflating the click rate to make the site look better or generate additional revenue). If such browsers are detected, they are often blocked and removed from the advertising counts, but may not be removed from the page counts. Again, it’s valid because we’re looking at website traffic and audiences from different perspectives.
You also need to account for the time it takes for the advertisement to be served. Advertisers generally prefer that ads be counted when the entire piece of copy or creative is delivered. If it’s one of those rich, interactive animations, it could be taking longer than you imagine for the file to be delivered. If the count occurs only after all content is delivered to the user’s browser, your ad system may not count the ad for a short period after it appears to have been shown. This is one to check with your ad-server technology vendor. When do they initiate the count?
Thus, your web analytics and your ad-impression counts may differ for valid reasons. The key is to ensure that, if you rely on advertising to fund your endeavours, you’re giving your advertising system the best chance of showing an advertisement in all the places you want them to appear. Make sure your content control systems are inserting the right codes in all the right places.
In summary, if you’re doing all the checks and your content systems are inserting the right codes, then your advertising system is doing the best job it can to count the advertisements for you. If it gives you a different number, then you shouldn’t worry too much – there’s an acceptable difference that you can work with.
Update: It’s taken me over two years to write one of the pieces I suggested above: the one about whether advertising is central to your offering, then you need to think about it in the design process. Read Get Your Product Right Or Get In The Liferaft for some insights.