CTR - The case study

“[...] user reactions to particular search results or search result lists may be gauged, so that results on which users often click will receive a higher ranking.”

“[...] using click and visit data to rank results is a very reasonable and logical thing to do, and ignoring the data would have been silly. [...] It's pretty clear that any reasonable search engine would use click data on their own results to feed back into ranking to improve the quality of search results. Infrequently clicked results should drop toward the bottom because they're less relevant, and frequently clicked results bubble toward the top.”

“In addition, click data (the website links on which a user actually clicks) is important for evaluating the quality of the search results page. As Google’s former chief of search quality Udi Manber testified:The ranking itself is affected by the click data. If we discover that, for a particular query, hypothetically, 80 percent of people click on Result No. 2 and only 10 percent click on Result No. 1, after a while we figure out, well, probably Result 2 is the one people want. So we’ll switch it.Testimony from Sergey Brin and Eric Schmidt confirms that click data is important for many purposes, including, most importantly, providing “feedback” on whether Google’s search algorithms are offering its users high quality results.”