We have found a close relationship between how many people search for flu-related topics and how many people actually have flu symptoms. Of course, not every person who searches for “flu” is actually sick, but a pattern emerges when all the flu-related search queries from each state and region are added together. We compared our query counts with data from a surveillance system managed by the U.S. Centers for Disease Control and Prevention (CDC) and discovered that some search queries tend to be popular exactly when flu season is happening. By counting how often we see these search queries, we can estimate how much flu is circulating in various regions of the United States.
On the subject of privacy, Google adds elsewhere, “We couldn’t have created such good models without aggregating hundreds of billions of individual searches going back to 2003. Of course, we’re keenly aware of the trust that users place in us and of our responsibility to protect their privacy. Flu Trends can never be used to identify individual users because we rely on anonymized, aggregated counts of how often certain search queries occur each week.”
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