Why might the estimated number of results change when going from page 1 to page 2?
Matt's answer:
Today’s question comes from San Francisco, California. Blind Five Year Old asks, “How reliable is the site colon query, and why does the total count sometimes change from page one to page two?” Well, I wouldn’t really put it in terms of the site colon query. Instead, I would pivot and narrow and focus down on the results estimates. So there’s a few things to know. Number one, if you haven’t noticed, you should notice that results estimates are only accurate to about three significant digits. So they are estimates. As we’re looking for queries, at some point we say, OK, we have enough to constitute the first page, and we see how far we’ve gone through our posting list– the amount of data we have– therefore, we can estimate there’s about this many results left. Now when you click from page one to page two, suddenly you’re going deeper. And so you have a better estimate or you have a slightly different estimate, because you’re starting to look not just a little bit of the way through all those documents, you’re actually starting to go deeper and deeper. So it’s relatively common for our results estimates to change going from page one to page two, typically becoming more accurate. So it’s not usually a factor of the site colon query. It’s usually a factor of us digging deeper through our data, and as a result, we have a better or at least a different estimate for how many results there are.
by Matt Cutts - Google's Head of Search Quality Team
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