Pearson's Correlation Coefficient Matrix of Three Influenza Surveillance Systems by US Census Region during the 2007-08 Influenza Season1,2

Note:1Because 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.2Overall mean Pearson's correlation coefficient by US Census Region during 2007-08 influenza season:a. Google Flu Trends and CDC ILI Surveillance: 0.97 (0.02)b. Google Flu Trends and CDC Virologic Surveillance: 0.87 (0.04)c. CDC ILI Surveillance and CDC Virologic Surveillance: 0.89 (0.05)3US 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.