Table 4. Performance of Google Flu Trends (GFT) relative to public health influenza-like illness (ILI) surveillance at the national (United States), regional (Mid-Atlantic States) and local (New York City) levels for specific epidemic and pandemic seasons.
| Time Period and Geographic Location | Original GFT model | Updated GFT model |
| R2 | R2 ('+/− week lag, max R2) | |
| National, United States | ||
| Influenza seasons 2003–2009 (prior to 2009 pandemic) | 0.88 | 0.92 |
| 2009 pandemic A/H1N1 early wave | 0.91 | 0.84 |
| 2009/2010 pandemic A/H1N1 season | NA | 0.98 |
| 2010/2011 season | NA | 0.95 |
| 2011/2012 season | NA | 0.88 |
| 2012/2013 season | NA | 0.90 |
| Regional, Mid-Atlantic States | ||
| Influenza seasons 2003–2009 (prior to 2009 pandemic) | 0.75 | 0.77 |
| 2009 pandemic A/H1N1 early wave | 0.51 | 0.82 |
| 2009/2010 pandemic A/H1N1 season | NA | 0.92 |
| 2010/2011 season | NA | 0.83 |
| 2011/2012 season | NA | 0.37 |
| 2012/2013 season | NA | 0.86 |
| Local, New York City | ||
| Influenza seasons 2003–2009 (prior to 2009 pandemic) | 0.87 | 0.84 |
| 2009 pandemic A/H1N1 early wave | 0.78 | 0.88 |
| 2009/2010 pandemic A/H1N1 season | NA | 0.51 (−3 wks, 0.89) |
| 2010/2011 season | NA | 0.74 (+1 wk, 0.80) |
| 2011/2012 season | NA | 0.80 |
| 2012/2013 season | NA | 0.94 |