Table 3. Pearson's Correlation Coefficient Matrix of Data from Three Influenza Surveillance Systems by US Census Region: Google Flu Trends, CDC Influenza-like Illness Surveillance, CDC Influenza Virologic Surveillance, September 28, 2003 through May 17, 20081.
| US Census Region2 | Dataset | Google Flu Trends | CDC ILI | CDC Virologic |
| New England | Google Flu Trends | 1.00 | -- | -- |
| CDC ILI | 0.94 (0.92, 0.96) | 1.00 | ||
| CDC Virologic | 0.65 (0.55, 0.73) | 0.76 (0.68, 0.82) | 1.00 | |
| Middle Atlantic | Google Flu Trends | 1.00 | -- | -- |
| CDC ILI | 0.87 (0.82, 0.90) | 1.00 | ||
| CDC Virologic | 0.67 (0.58, 0.75) | 0.70 (0.61, 0.77) | 1.00 | |
| East North Central | Google Flu Trends | 1.00 | -- | -- |
| CDC ILI | 0.96 (0.94, 0.97) | 1.00 | ||
| CDC Virologic | 0.64 (0.54, 0.72) | 0.73 (0.65, 0.80) | 1.00 | |
| West North Central | Google Flu Trends | 1.00 | -- | -- |
| CDC ILI | 0.95 (0.93, 0.97) | 1.00 | ||
| CDC Virologic | 0.80 (0.74, 0.85) | 0.82 (0.76, 0.87) | 1.00 | |
| South Atlantic | Google Flu Trends | 1.00 | -- | -- |
| CDC ILI | 0.91 (0.88, 0.93) | 1.00 | -- | |
| CDC Virologic | 0.72 (0.64, 0.79) | 0.82 (0.76, 0.86) | 1.00 | |
| East South Central | Google Flu Trends | 1.00 | -- | -- |
| CDC ILI | 0.81 (0.75, 0.86) | 1.00 | -- | |
| CDC Virologic | 0.69 (0.60, 0.76) | 0.64 (0.55, 0.73) | 1.00 | |
| West South Central | Google Flu Trends | 1.00 | -- | -- |
| CDC ILI | 0.87 (0.82, 0.90) | 1.00 | -- | |
| CDC Virologic | 0.74 (0.70, 0.80) | 0.86 (0.81, 0.89) | 1.00 | |
| Mountain | Google Flu Trends | 1.00 | -- | -- |
| CDC ILI | 0.91 (0.88, 0.93) | 1.00 | -- | |
| CDC Virologic | 0.72 (0.64, 0.79) | 0.81 (0.75, 0.86) | 1.00 | |
| Pacific | Google Flu Trends | 1.00 | -- | -- |
| CDC ILI | 0.84 (0.79, 0.88) | 1.00 | -- | |
| CDC Virologic | 0.67 (0.58, 0.75) | 0.78 (0.71, 0.83) | 1.00 |
Note:
Because CDC surveillance is intensified from calendar week 40 through calendar week 20 of the subsequent year, we restricted our correlation analyses to this time period.
US Census Regions include the following states: (1) New England – Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, Vermont; (2) Middle Atlantic – New Jersey, New York, Pennsylvania; (3) East North Central – Indiana, Illinois, Michigan, Ohio, Wisconsin; (4) West North Central – Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, South Dakota; (5) South Atlantic – Delaware, District of Columbia, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, West Virginia; (6) East South Central – Alabama, Kentucky, Mississippi, Tennessee; (7) West South Central – Arkansas, Louisiana, Oklahoma, Texas; (8) Mountain – Arizona, Colorado, Idaho, New Mexico, Montana, Utah, Nevada, Wyoming; (9) Pacific – Alaska, California, Hawaii, Oregon, Washington.