Table 1. Comparing estimates of the weekly percentage of physician visits related to influenza-like illness (ILI) based on Google Flu Trends (GFT) to values reported by the Centers for Disease Control and Prevention (CDC), United States, October 2010–March 2014.
| Estimate | 2010–13 seasons(Week 40, 2010 to Week 30, 2013)* | 2013–14 season(Week 31, 2013 to Week 10, 2014)* | ||||||||
| No. (%)above baseline weeks** within ±5% | No. (%)above baselineweeks within ±10% | Sum of squared errors | Relative % difference in peak magnitude (2012–13) | Difference in peak timing (2012–13) | No. (%)above baselineweeks† within ±5% | No. (%)above baselineweeks within ±10% | Sum of squared errors | Relative % difference in peak magnitude | Difference in peak timing | |
| Original2009%GFT | 0 (0.0) | 2 (6.9) | 177.4 | 74.1 | 3 weeks after | - | - | - | - | - |
| Recalibrated 2013%GFT | - | - | - | - | - | 6 (43) | 8 (57) | 3.8 | 9.1 | 1 week after |
| Preliminary %ILINet from previous week | 8 (28) | 12 (41) | 17.0 | - | - | 2 (14) | 5 (36) | 5.7 | - | - |
| Transformed%GFT (c = 0.65) | 8 (28) | 17 (59) | 12.1 | –2.2 | 1 week after | 5 (36) | 11 (79) | 2.1 | −1.3 | 1 week after |
| Transformed %GFT (c = 1.1) | - | - | - | - | - | 6 (44) | 10 (71) | 1.6 | 2.4 | 1 week after |
*Week 39 of 2010 and week 30 of 2013 were used to calculate transformed %GFT estimates for each of these time periods, respectively.
**During the 2010–13 seasons, 29 weeks were above baseline.
†
During the 2013–14 season, 14 weeks were above baseline.