340.721 Epidemiologic Inference in Public
Health Exam Questions and Answers
Question 1
Which of the following statements is(are) true of using a less strict case
definition as compared to a more strict case definition? (SELECT ALL THAT
APPLY)
a. More individuals who truly are ill will be counted as cases
b. More individuals who truly are ill will be counted as non-cases
c. More individuals who truly are not ill will be counted as non-cases
d. More individuals who truly are not ill will be counted as cases
DESCRIBE THE STUDY POPULATION AT RISK
In addition to identifying a case definition, you must decide who to include in
your study. Ideally, you would obtain measurements on everyone who was at
risk of becoming ill.
Question 2
The term ‘at risk’ is defined as those individuals who are able become ill in
the same way. Which of the following groups can be considered ‘at risk’ in
this outbreak if we believe the outcomes are due to a food-related illness?
a. All members and their families
b. All members and guests who attended the luncheon
c. All members and guests who attended the luncheon and ate
d. All members and guests who attended the luncheon, ate, and
reported having symptoms
Recall that a questionnaire was prepared by the Health Department and
[1]
,distributed one week after the luncheon to all members and to as many
guests as possible in order to obtain clinical details of the illness. Table 1
summarizes the responses from members and from guests.
Table 1. Summary of Response to the Questionnaire for Members and Guests
Members Guests
Number of people to whom As many as possible
90
questionnaires were sent (Assume ~800)
Number of responses
86 67
from attendees
Number of responses from 85 67
attendees who ate
Number of people who 60 57
reported sore throat
Number of people who 41 48
reported sore throat and
fever
From Table 1, 90 members were asked to complete the questionnaire. 86
of those 90 members returned the questionnaire. The questionnaire
response rate for members is therefore:
Response rate = # of members that completed the questionnaire 86
= = 0.96, or 96%
# of members who were asked to complete the questionnaire 90
Question 3
What is the response rate for guests?
a. 8%
b. 46%
c. 72%
d. 85%
(NOTE: Are you wondering why you were asked to calculate the response
rate? Compare the response rate you calculated for guests in Question 3 to
the 96% response for members. Are they similar or different? What are
some possible reasons why?
[2]
, If you are unable to obtain measurements on everyone, a more practical
goal is to obtain measurements from a representative group of all the people
at risk of becoming ill. Based on the response rates, which group do you
think is more representative – members or guests?)
ATTACK RATES
The attack rate is an example of a measure of disease frequency. It is
calculated as the number of people at risk in whom a certain illness
develops divided by the total number of people at risk. Using a case
definition of sore throat and a study population that includes only ‘at risk’
members the overall Attack Rate in members is:
𝐴𝑡𝑡𝑎𝑐𝑘 𝑟𝑎𝑡𝑒 = = # of members who attended the luncheon and ate and who then reported sore throat
60
# of members who attended the luncheon and ate
= = 0.706, 𝑜𝑟 70.6%
85
[3]
Health Exam Questions and Answers
Question 1
Which of the following statements is(are) true of using a less strict case
definition as compared to a more strict case definition? (SELECT ALL THAT
APPLY)
a. More individuals who truly are ill will be counted as cases
b. More individuals who truly are ill will be counted as non-cases
c. More individuals who truly are not ill will be counted as non-cases
d. More individuals who truly are not ill will be counted as cases
DESCRIBE THE STUDY POPULATION AT RISK
In addition to identifying a case definition, you must decide who to include in
your study. Ideally, you would obtain measurements on everyone who was at
risk of becoming ill.
Question 2
The term ‘at risk’ is defined as those individuals who are able become ill in
the same way. Which of the following groups can be considered ‘at risk’ in
this outbreak if we believe the outcomes are due to a food-related illness?
a. All members and their families
b. All members and guests who attended the luncheon
c. All members and guests who attended the luncheon and ate
d. All members and guests who attended the luncheon, ate, and
reported having symptoms
Recall that a questionnaire was prepared by the Health Department and
[1]
,distributed one week after the luncheon to all members and to as many
guests as possible in order to obtain clinical details of the illness. Table 1
summarizes the responses from members and from guests.
Table 1. Summary of Response to the Questionnaire for Members and Guests
Members Guests
Number of people to whom As many as possible
90
questionnaires were sent (Assume ~800)
Number of responses
86 67
from attendees
Number of responses from 85 67
attendees who ate
Number of people who 60 57
reported sore throat
Number of people who 41 48
reported sore throat and
fever
From Table 1, 90 members were asked to complete the questionnaire. 86
of those 90 members returned the questionnaire. The questionnaire
response rate for members is therefore:
Response rate = # of members that completed the questionnaire 86
= = 0.96, or 96%
# of members who were asked to complete the questionnaire 90
Question 3
What is the response rate for guests?
a. 8%
b. 46%
c. 72%
d. 85%
(NOTE: Are you wondering why you were asked to calculate the response
rate? Compare the response rate you calculated for guests in Question 3 to
the 96% response for members. Are they similar or different? What are
some possible reasons why?
[2]
, If you are unable to obtain measurements on everyone, a more practical
goal is to obtain measurements from a representative group of all the people
at risk of becoming ill. Based on the response rates, which group do you
think is more representative – members or guests?)
ATTACK RATES
The attack rate is an example of a measure of disease frequency. It is
calculated as the number of people at risk in whom a certain illness
develops divided by the total number of people at risk. Using a case
definition of sore throat and a study population that includes only ‘at risk’
members the overall Attack Rate in members is:
𝐴𝑡𝑡𝑎𝑐𝑘 𝑟𝑎𝑡𝑒 = = # of members who attended the luncheon and ate and who then reported sore throat
60
# of members who attended the luncheon and ate
= = 0.706, 𝑜𝑟 70.6%
85
[3]
