Reassessing Google Flu Trends Data for Detection of Seasonal and Pandemic Influenza: A Comparative Epidemiological Study at Three Geographic Scales
Figure 2
Scatter plots of weekly excess influenza-like illness (ILI) visit proportions against original Google Flu Trends (GFT) model search query estimates, 2003–2009.
Weekly excess percent-ILI is calculated as Serfling estimates subtracted from observed proportions. Plots show original GFT model estimates compared with weighted CDC ILI-Net data for (A) the United States, and (B) Mid-Atlantic Census Region States (New Jersey, New York, Pennsylvania), and local ILI surveillance from emergency department visits for (C) New York City. Plots are shown for pre-pandemic influenza seasons, June 1, 2003 to April 25, 2009 (grey circles) and the early wave of the A/H1N1 pandemic, April 26 to August 1, 2009 (red diamonds). Lines representing equivalent axes for X = Y are shown (grey dashed line). Regression lines are shown for seasonal influenza 2003–2009 (black line) and the early 2009 wave of the pandemic (red line).