ILI-activity can have significant regional variation, so regional ILInet data was used as the target.

FORBES: How Accurate Is Google Flu Trends?

Unlike ILInet, the estimates are produced from a model that uses the activity of certain search terms on Google Websearch.

FORBES: How Accurate Is Google Flu Trends?

Similar to ILINet, Flu Trends produces estimates of Influenza-like Illness.

FORBES: How Accurate Is Google Flu Trends?

Those that correlated best with the ILInet data were selected.

FORBES: How Accurate Is Google Flu Trends?

ILI-activity also varies significantly from season to season, both in its timing and severity, so we used ILInet data from 2003 to the most recent data points available at the time.

FORBES: How Accurate Is Google Flu Trends?

Additionally, the chance of a random search term correlating with the ILInet data in all ten regions is considerably less than the chance that a random search term can correlate with the data for single location.

FORBES: How Accurate Is Google Flu Trends?

Each has strengths and weaknesses and thus to monitor influenza activity in the United States, the CDC runs both a syndromic system (called ILInet, short for Influenza-like Illness network) and a virologic system (part of a larger system called NREVSS).

FORBES: How Accurate Is Google Flu Trends?

Of course, this ED syndromic network for New York City is not the same as ILInet for New York City, New York City is not representative of the United States as a whole and the flu season is far from over.

FORBES: How Accurate Is Google Flu Trends?