Mortality data were smoothed using a 17-day leading moving average (e.g., mortality on January 1 is the mean from January 1-17). This smoother was selected after testing a variety of filter lengths and based upon prior research [6] . We examined both daily P&I mortality ''events'' and longer mortality ''episodes.'' ''Events'' are days with (smoothed) mortality at least one standard deviation above the long-term (smoothed) mean for that date. This z$1 criterion was chosen because the frequency distribution of smoothed mortality is positively skewed with the tail beginning at approximately one standard deviation. After smoothing, there is an obvious tendency for high mortality events to cluster into prolonged periods when the z$1 threshold is (Figure 2 ). We thus identified 12 P&I mortality episodes over the 28-year period of record (Table 2) .