Fig. 2

Yearly age-stratified incidence rates for age-supplied reported cases (\( \hat{\ {\boldsymbol{R}}_{\boldsymbol{j}}} \)) and “Unknown” group \( \hat{{\boldsymbol{R}}^{\boldsymbol{U}}} \). Note that some of the age groupings changed during the years of reporting; these changes are denoted by gaps in the graph. Contrary to Fig. 1, the incidence rate for age-unknown cases is comparatively small throughout, since its denominator is the entire population rather than just one age group