Table 2. Correlation and RMSE between United States Google Flu Trends estimates and ILINet data.
Pre-pH1N1(September 2003–March 2009) | pH1N1 Overall(March 2009–December 2009) | pH1N1 Wave 1(March 2009–August 2009) | pH1N1 Wave 2(August 2009–December 2009) | |
Correlation | ||||
Original Model | 0.906 | 0.912 | 0.290* | 0.916 |
Updated Model | 0.942 | 0.989 | 0.945 | 0.985 |
RMSE | ||||
Original Model | 0.006 | 0.018 | 0.008 | 0.023 |
Updated Model | 0.005 | 0.005 | 0.001 | 0.007 |
*The overall correlation during pH1N1 is not an average of the Waves 1 and 2 correlations. The range of ILI rates was larger in Wave 2 than in Wave 1, causing the Wave 2 data to contribute more than the Wave 1 data to the overall correlation during pH1N1.