Figure 4. Age-specific pneumonia and influenza (P&I) excess death rates in the 1951 influenza epidemic, 1957, and 1968 pandemics, Canada. A) Observed. B) Exponential models using 5-year age groups starting at age 55 years and ending at >90 years (R2 >0.85 for all seasons). Black curve: "null distribution" of expected pattern in epidemic seasons, based on major epidemics in the interpandemic periods, 1950–1999 (N = 17). The age coefficient was set at the mean of the "null" distribution (see Table 3 for values). The intercept was set at the minimum of the distribution for legibility.