# Incidence density

Suppose there are $6$ people in a population. During $2$ weeks $3$ people get the flu. Cases of the flu last $2$ days. Also people will get the flu only once during this period. What is the incidence density of the flu?

Would it be $\frac{3}{84 \text{person days}}$ since each person is observed for $14$ days?

• Do you know when each people get the flu? – ThiS Jan 24 '13 at 13:25
• @Thierry: Assume that they get the flu on Monday, Tuesday, and Wednesday of the first week. – user20032 Jan 24 '13 at 15:13
The true incidence is $\frac{3}{(3*14)+(7+8+9)} = \frac{3}{66 person-days}$.