One of the core metrics online marketers use is the number of impressions an advertisement receives.   That’s important in any advertising, but the prices advertisers pay for search advertising is based in part on the “click through rate” or CTR. Today’s Google Instant announcement means that search results will change fast and that’s very cool.  You’ve undoubtedly seen media coverage or even used the search yourself.

The biggest browsers:  Firefox, IE 8,  Chrome and Safari will all use Google’s instant search. But the impression counts are going to be completely shot. As the announcement was being made, I asked two well known online marketers on Twitter what would happen to the impression count.  You see, every time a new set of ads was displayed, Google’s counters likely considered each ad displayed and incremented the impression count. One’s response? “Good question” Inside AdWords, the official Google AdWords blog, admitted this afternoon that impression counts will vary.  Here’s the quote from Dan Friedman there:

It’s possible that this feature may increase or decrease your overall impression levels. However, Google Instant may ultimately improve the quality of your clicks since it helps users type queries that more directly connect them with the answers they need.

Feel free to stop reading after the first sentence. Those fancy reports you look at every day or week or month?  The ones that folks like us look at daily?  One of the key measures–impression count–is shot.  Everything derived from that measure, including click through rate, is suspect. It’s not that the usability is good or bad or that the metrics themselves are good or bad.  Your takeaway as a small business leader is that some of your key measurements are no longer apples.  They’re oranges. And that means your online advertising history will be like comparing two different fruits.