Oakland outlier. The plot of residuals in Exercise 41 shows large f luctuations starting in 2006 and an earlier outlier that wasn’t as evident in the data. The outlier is September 2001. This wasn’t a typical month for air travel because of the 9/11 attacks. Here are three models fit to the series up through 2006; a single exponential smooth, a 12-point moving average, and the fitted values from a seasonal regression model. Discuss how each deals with the outlier.