1. You are working in the public health unit of a university town and monitoring gastrointestinal (GI) illness in 4000 university students living in residence. You collect data showing that 175 students had an GI illness in 2022, 150 students developed a new GI illness in 2022, 50 students had a GI illness sometime during the month of December, and 20 were sick with a GI illness at the start of the exam period (December 9, 2022).

Show all steps of your calculations, including formulae, and be sure to provide a summary sentence for each question, stating your results in full.

1. What is the incidence of GI illness in this student population in 2022?
2. What is the period prevalence for GI illness in this student population in 2022?
3. What is the point prevalence for GI illness in this student population on the first day of exams (December 9, 2022)?