1. Between 2012 and 2013, the average annual number of new colorectal cancer cas
ID: 3069769 • Letter: 1
Question
1. Between 2012 and 2013, the average annual number of new colorectal cancer cases in Holmes County, MS was 17. In that same time period, the average number of colorectal cancer cases for Hinds County, among all residents, was 134. Based on these data, is it accurate to say that the incidence rate is higher in Hinds County than in Holmes County? Why or why not? (2 points) 2. Consider that you have a population composed of 200 CDC scientists that you are following for one year During follow-up, twenty-five (25) scientists developed symptoms consistent with inhalation anthrax disease Laboratory testing confirmed that they were in fadt infected with Bacillus anthracis. a) What are the incident cases of inhalation anthrax during the follow-up year? (1 point) b) What is the population at risk for anthrax at the start of the follow-up year? (1 point) c) Calculate the cumulative incidence of anthrax in this situation. (1 point) 3. Before the start of a study the researchers screen 30,000 people for disease. Of these, 250 have the disease in question. What is the prevalence of the disease per 1000 people? (1 point) 4. In the same study as above (see question number 3), the study starts with only those people who were found free of disease at the screening. Over the next 2 years 200 develop the disease. What is the incidence rate of the disease over the study period? Assume that persons with new diagnoses of disease contribute only one year towards the denominator. (1 point)Explanation / Answer
1.
The incidence rate is a measure of the number of new cases ("incidence") per unit of person-time ("rate").
If the population of Hinds County is larger than Holmes County, then it is possible to have high number of new cases of colorectal cancer in Hinds County as compared with Holmes County.
Also, the total amount of time "at risk" of the subjects of Hinds County would be larger than Holmes County.
So, both the numerator and denominator part of incidence rate for Hinds County is larger than Holmes County.
Thus, it is possible that the incidence rate is same for Hinds County and Holmes County.
It is not accurate to say that the incidence rate is higher in Hinds county than in Holmes County.
2.
a) The incident cases of inhalation anthrax during the follow-up year is 25.
b) The population at risk for anthrax at the start of the follow-up year is 200 CDC scientists.
c) Cumulative Incidence = (# new cases reported during the year) / (population at risk)
= 25 / 200 = 0.125
3.
If 250 of the people were suffering from disease initially, then the prevalence of disease at this point in time would be 250/30000 =
0.008333333 = 0.008333333 * 1000 per 1000 people
= 8.33 per 1000 people
4.
Number of people with no disease = 30000 - 250 = 29750
As, each person contributed only one year towards the denominator
Number of person years = 29750 * 1 = 29750 person-years
Incident rate = Number of new cases / Number of person-years
= 200 / 29750
= 0.006722689 per person-year
= 6.72 per 1000 person-year
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