Incidence Density:
New cases = 3; period of time at risk of developing the disease = 33 individuals / years
x = 3 * 100/33 = 9.1 cases / 100 individuals year
The cumulative incidence:
number of new cases in the population at risk = 3; number of people free of the disease at the beginning of the study = 7;
x = 3 * 100/7 = 43 cases per 100 people for 7 years
The average duration
total number of years with the disease = 13; number of cases = 3
dm = 13/3 = 4.3 years
Prevalence
number of sick people = 2; number of people exposed = 6
P = 2 * 100/6 = 33.3 = 33 cases / 100 people
Lethality
number of deaths = 1, number of cases = 3
l = 1 * 100/3 = 33.3%
