Solution
= Solution
The crude incidence-rate estimator is
$$
\widehat q_{SE}=\frac{10}{1000\times3}=\frac1{300}
$$
per person-month. This treats all 3000 person-months as susceptible time and assumes infection times are observed exactly, follow-up is complete, and each first infection is detected. In practice tests occur intermittently, so infection is <interval censoring>[interval-censored]; latent, brief, or asymptomatic infections may also be missed.