Question

Problem 4: Distinguishing between Point and Period Prevalence, Cumulative Incidence and Incidence Density at Happy Kids Day Care Center (11 points)

There were 11 children enrolled in the Happy Kids Day Care Center from the beginning of Month One until the end of Month Four. The 11 children were watched for a total of 4 months. The staff tries to keep good records about when children fall ill from disease X.

Child	Month 1		Month 2		Month 3		Month 4
1
2
3
4
5
6
7
8
9
10
11

               

You are asked to inspect these records and report the following information. The information has been assembled in the figure above. The grey bar indicates the disease is present. For ease of calculations consider one month is equal to 30 days and disease begins on either the 1^st or 15^th of the month, except for Child #1 who was already ill when record-keeping began. Show all steps, including numerator and denominators. Express all final answers as percentages (multiplier of 100).         

1. Calculate the point prevalence of disease X at the end of Month 4. (2 points)
2. Calculate the period prevalence of disease X for the entire four months. (2 points)

Answer 1

Point prevalence is the proportion of a population that has the condition at a specific point in time.

The point prevalence of disease X at the end of Month 4=(the number of children having disease X at the end of Month 4)/ (total number of children enrolled)

Here,the number of children having disease X at the end of Month 4=7

Total number of children enrolled=11

Therefore,the point prevalence of disease X at the end of Month 4=7/11=0.6363

The point prevalence of disease X at the end of Month 4 in terms of percentage =(7/11)*100=63.63%

Period prevalence is the proportion of a population that has the condition at some time during a given period and includes people who already have the condition at the start of the study period as well as those who acquire it during that period.

The period prevalence of disease X for the entire four months=(the number of children having disease X in the period of that 4 months)/ (total number of children enrolled)

the number of children having disease X in the period of that 4 months(in terms of person-months)= 1+0+(5/8)+(4/8)+0+0+(6/8)+(2/8)+0+(5/8)+(7/8)=4.625

total number of children enrolled=11

The period prevalence of disease X for the entire four months=4.625/11=0.4204

The period prevalence of disease X for the entire four months in terms of percentage =(4.625/11)*100=42.04%