A University of Washington study which compares Google Flu Trends estimates of flu activity with estimates from the Centers for Disease Control and Prevention says “Google Flu Trends is about 25% less accurate at estimating flu rates.” “Historically, we’ve shown a strong correlation with CDC’s ILINet data, typically with a correlation of greater than 0.9 (or more than 90% accurate. Recent study shows that Google Flu Trends is 72% accurate as compared with CDC's Virologic Surveillance data. This doesn't come as much of a surprise since virologic data is telling a different story than ILInet data. However, it’s good to see research showing differences in these measures, as it highlights the need for multiple networks to exist,” writes Google.
“Google Flu Trends influenza surveillance provides an excellent public health service, because it provides nationwide influenza activity data in a cheap and timely manner,” said Dr. David Ortiz. “Nevertheless, our study demonstrates that its data should be interpreted with caution and that other surveillance systems more accurately reflect influenza activity in the United States.”