Question

PROBLEM 1. (6 points) Figure 1, below represents 10 new cases of illness in a population of 20 persons over a period of 15 months. Each horizontal line represents the period of time one person spends beingi. The down arrow indicates the date of onset of illness. The solid line represents the duration of illness. The up arrow and the cross represent the date of recovery and date of death, respectively FIGURE 1. New Cases of lllness from October 1, 2004-September 30, 2005 Date of onset of illness Date of death Date of recovery Person # 1 2 3 4 5 7 8 10 Oct. 1, 2004 Apr. 1, 2005 Sept. 30, 2005

Calculate the incidence rate from October 1, 2004, to September 30, 2005, using the midpoint population (population alive on April 1, 2005) as the denominator. Express the rate per 100 population.

Show the formula, calculations and the interpret the results

Answer 1

Incidence rate = (number of new cases/ number of people in that the time interval) X 100

so there are four new cases(persons-3,6,7 and 10) in between october 1 2005 to september 30 2005.

There are 20 people in the study, and 2 people died before april1st (Person 2 and person 8), so the number of people in the study at that time period is 18

Incidence rate = (4 ⁄ 18) × 100
= 22 new cases / 100 people