Average excess P&I mortality rates per 100,000 in Japanese and US seniors aged 65–89 yrs, 1978–2006.

Standard deviations are tabulated in parentheses. Percent changes were calculated as the mean mortality rate in 1995–2006 (the period after discontinuation of the Japanese schoolchildren vaccination program) minus that in 1978–1994 (the schoolchildren vaccination program period in Japan), divided by the mean mortality rate in 1978–1994. P-values were determined using Wilcoxon's Rank Sum Test. Adjusted estimates were standardized to the US population structure of 2000 and corrected for time trends in the baseline risk of mortality (see Methods).