Google’s Chief Economist Hal Varian said during a Google Tech Talk on October 22, 2012 that Google users may see a dozen or more Google experiments per Google visit.
About 26 minutes into the Google Tech Talk, Hal said, “any time you access Google, you probably are in a dozen or more experiments.”
The talk was about how companies handle “big data,” such as testing various experiments and how to measure those results. So Hal gave an example that a single user may see a dozen or more experiments each time they use Google.
Google has gone on record with us dozens of times that they release about 500 updates to search per year. Hal went on to explain that they do 5,000 experiments in a year. On the ad side they may do 500 changes per year, like on the organic side.
Here is the video, skip to about 26 minutes in to jump to the specific point of this discussion: