Optimizing Provider Recruitment for Influenza Surveillance Networks
Figure 3
Statewide influenza activity mirrors population distribution.
(a) Shading indicates zip code level population sizes, as reported in the 2000 census. (b) Major populations centers exhibit covariation in influenza activity. We performed a principal component analysis (PCA) on the centered hospitalization time series of all zip codes and calculated the time series of the first principal component. Zip codes are shaded according to the obtained from a regression of the first principal component time series to the influenza hospitalization time series for the zip code. Dark shading indicates high synchrony between influenza activity in the zip code and the first principal component. The correspondence between darkly shaded zip codes in (a) and (b) results from the high degree of synchrony in influenza activity between highly populated zip codes in Texas.