HSA 550 PBSC Contingency Tables and Odds Ratio Questions – Description
1. The data in the table below describes characteristics of the 38 persons who ate food at or from a church
supper in Texas in August 2001. Fifteen of these persons later developed botulism.
Attended Date of Ate Ate Ate Ate
ID Age Supper Case Onset Case Status Any Food Chili Chicken Spinach
1 1 Y N – Y Y Y N
2 3 Y Y 8/27 Lab-confirmed Y Y N Y
3 7 Y Y 8/31 Lab-confirmed Y Y N N
4 7 Y N – Y Y Y N
5 10 Y N – Y Y N Y
6 17 Y Y 8/28 Lab-confirmed Y Y Y N
7 21 Y N – N N N N
8 23 Y N – Y Y N N
9 25 Y Y 8/26 Epi-linked Y Y N N
10 29 N Y 8/28 Lab-confirmed Y N N Y
11 38 Y N – N N N N
12 39 Y N – N N N N
13 41 Y N – Y Y Y N
14 41 Y N – N N N N
15 42 Y Y 8/26 Lab-confirmed Y Y Y N
16 45 Y Y 8/26 Lab-confirmed Y Y Y Y
17 45 Y Y 8/27 Epi-linked Y Y Y N
18 46 Y N – Y N Y N
19 47 Y N – Y N Y N
20 48 Y Y 9/1 Lab-confirmed Y Y N N
21 50 Y Y 8/29 Epi-linked Y Y N N
22 50 Y N – Y N Y N
23 50 Y N – Y N N Y
24 52 Y Y 8/28 Lab-confirmed Y Y Y N
25 52 Y N – N N N N
26 53 Y Y 8/27 Epi-linked Y Y Y N
27 53 Y N – Y Y N N
28 62 Y Y 8/27 Epi-linked Y Y Y N
29 62 Y N – Y N Y N
30 63 Y N – N N N N
31 67 Y N – N Y N N
32 68 Y N – N N N N
33 69 Y N – Y Y Y N
34 71 Y N – Y N Y N
35 72 Y Y 8/27 Lab-confirmed Y Y Y N
36 74 Y N – Y Y N N
37 74 Y N – Y Y Y N
38 78 Y Y 8/25 Epi-linked Y Y Y N
a. Construct a 2×2 contingency table (see textbook p. 47) of the disease by exposure to chicken.
b. Construct a 2×2 contingency table (see textbook p. 47) of the disease by exposure to chili.
c. Construct a 2×2 contingency table (see textbook p. 47) of the disease by exposure to Spinach.
I
2. The use of cellular phones has been associated with the development of brain cancer, as evidenced in
several studies. However, other studies have shown no such association. The table below includes the
results of a case–control study of brain tumors and the regular use of cellular phones. This study was
conducted using a control group made up of a random sample of the population of high school students
who attended the same schools where the students with brain tumors were found.
Brain Tumors No Brain Tumors
Cell Phones 63 85
No Cell Phones 96 292
a. How many study subjects were cases?
b. How many study subjects were controls?
c. What was the ratio of controls to cases?
d. Calculate the odds ratio that compares exposure to cellular phones among those with and
without the disease.
e. Make a conclusion based on the calculated odds ratio
3. Consider the risk of developing breast cancer for women related to the age which they had their first child.
First Child at Breast Cancer No Breast Cancer
Age 25 or older
Yes 34 1,597
No 65 3,452
a. Calculate the odds ratio.
b. What does this value mean?
4. A cohort study was conducted to study the association of coffee drinking and anxiety in a population-based
sample of adults. Among 10,000 coffee drinkers, 500 cases of anxiety were observed. Among 20,000
adults who do not drink coffee, 200 cases of anxiety were observed.
a. Construct a 2×2 contingency table for the data.
b. What is the relative risk of anxiety associated with coffee use?
c. What does this value mean?
5. Of 2,472 people who had received radiation treatment in childhood because of enlarged thymus, cancer of
the thyroid developed in 24 and benign thyroid tumor developed in 52. A comparison group consisted of
3,055 children who had received no such treatment (brothers and sisters of those who had received
radiation treatment). During the follow-up period, one of the comparison group developed thyroid cancer,
but benign thyroid tumors developed in 6.
a. Construct TWO 2×2 contingency tables for the data. One is for thyroid cancer and the other
table is for benign thyroid tumors.
b. Calculate the relative risk for benign thyroid tumors. Calculate the relative risk for thyroid
cancer.
c. Explain the results
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