[Illustration: District 4 Influenza 1918–19 Case Rate per 100 persons by sex and age District 5 Influenza 1918–19 Case Rate per 100 persons by sex and age District 6 Influenza 1918–19 Case Rate per 100 persons by sex and age] CHART XXI. [Illustration: District 1 Influenza 1920 Case Rate per 100 persons by age periods District 2 Influenza 1920 Case Rate per 100 persons by age periods District 3 Influenza 1920 Case Rate per 100 persons by age periods] [Illustration: District 4 Influenza 1920 Case Rate per 100 persons by age periods District 5 Influenza 1920 Case Rate per 100 persons by age periods District 6 Influenza 1920 Case Rate per 100 persons by age periods] _Relationship of sex to severity._—In classifying cases as to severity, we have followed the standard previously described. Our results have shown that the 1920 recurrence in our group of individuals has been decidedly milder than the earlier 1918 spread. The proportion of mild cases in 1920 is nearly twice that of mild attacks in 1918–19. The proportion of severe cases was twice as great in 1918 as in 1920. The actual severity in 1918 was even greater than would be indicated by these figures. The last column in Chart XVIII is a combination of the two preceding, and while the 1920 column includes all classed as severe, pneumonia, and fatal, that for 1918 only includes the severe and pneumonia cases, but does not include the fatal cases for that year, because those who died during the 1918–19 epidemics are not counted in our 10,000 individuals surveyed. If these were included the percentage of total severe, or average severity would be greater than 42.70. We find that in 1918 the female sex had a higher proportion of severe cases according to our standard than did the male. This was equally true in 1920. We should emphasize here that we are not comparing only the fatal cases in the two sexes, but all classified as severe, and including fatal in 1920. Not only was the female sex attacked in slightly greater proportion, but also the individual cases appear to have been on the aggregate somewhat more severe in that sex. _Morbidity by age._—Before discussing the incidence of influenza in the various age periods we should explain that the charts for 1920 are based on the ages given by the individuals, and those for 1918 upon these ages, corrected by the subtraction of 15 months from the age as given. In our study of cases recurring during both epidemics the age used in the calculations is that of 1920. It is for this reason that in all of our age charts we have a first age period from zero to 15 months. Infants of less than 15 months at the time of our survey were born subsequent to the peak of the 1918–19 epidemic, and are not included in computations for that time.