A rolling analysis was employed to compare the models in a predictive scenario. Initially, a series of length j = 1, …, n = 150 weeks in s = 53 counties is used to predict the influenza rate in the next two weeks, n + 1 and n + 2. The rolling is then performed along the epidemic periods (J = 28 weeks, from week 40 to week 15 next year) by computing the mean square predictive error: MSPE=1J∑j=n+1n+J∑r=1swr(Ratej,r-Rate^j,r)2 where wr is the weight (in terms of pop) for county r. For ease of simplicity, the GLS setting is only considered with an AR(1) specification of the dependence structure, whereas the iGLS is combined with an AR(1), AR(2) and AR(p).