Assignment:
Note. This assignment is to be done alone with you as the sole author. Any work that appears to have been done in groups or with a partner will receive a zero.
For any calculations, please show all of your work to receive partial credit.
1. Please label the following statements as true (T) or false (F) regarding bias in epidemiologic research.
a. ___Bias is an error in design or execution of a study that produces results that are consistently distorted in one direction and lead to an incorrect assessment of the association between the factor and the disease under study.
b. ___Bias could be due to problems in the selection of the population to be studied.
c. ___Bias can be prevented or minimized by taking a larger sample.
d. ___Two major types of bias are selection bias and information bias.
e. ___Sample error is a type of bias where the obtained sample values (sample statistics) differ from the values
2. An investigator would like to assess the association of melanoma (skin cancer) and exposure to infrared skin tanning services by using a hospital-based case-control study. Hospitalized individuals with melanoma will be compared to hospitalized patients without melanoma (controls). This hospital is located in a low-income area of the city and is famous nationwide for its expertise in melanoma; individuals with melanoma (cases) from all over the country go to that hospital to get the highest quality care that can be provided. However, this hospital is not as well known for other medical conditions. Therefore, cases would come from all over the country and controls will be mostly local low-income individuals. The investigator predicts that an overestimation of the association between melanoma and skin tan services may occur. Please label the following statements as true (T) or false (F) regarding this study.
a. ___The investigator is wrong, an underestimation of the association is more likely to occur.
b. ___The results of this study are likely to be influenced by information bias.
c. ___The results of this study are likely to be influenced by selection bias.
d. ___Recall bias is likely to be present in this study.
e. ___Bias caused by misclassification of the outcome (namely melanoma) is likely to be a major problem.
3. To determine whether baldness causes coronary heart disease (CHD) in men, a hypothetical cohort study was carried out. The epidemiologist in charge of the study recruited 10,000 bald men and 10,000 men with hair into the study and followed all of them for 10 years to determine whether they developed CHD. Results are shown below.
|
|
CHD
|
Total
|
|
Yes
|
No
|
|
Bald
|
775
|
9,225
|
10,000
|
|
Hairy
|
190
|
9,810
|
10,000
|
|
Total
|
965
|
19,035
|
20,000
|
a. Calculate the risk of CHD among bald men.
b. Calculate the risk of CHD among hairy men.
c. What is the relative risk of CHD associated with baldness? Briefly explain how to interpret the value you calculated.
d. Does this result suggest that baldness may be a cause of CHD? What alternate explanation can you provide?
e. The investigator thought that the results might be confounded by age. What is meant by "confounded by age" in the context of this example?
4. The investigator stratified the results, displaying them separately for the older subjects (aged 65 and over) and the younger subjects (aged 40-64). Examine the two tables that follow.
CHD among Older Participants
|
|
CHD
|
Total
|
|
Yes
|
No
|
|
Bald
|
775
|
6,750
|
7,500
|
|
Hairy
|
100
|
900
|
1,000
|
|
Total
|
850
|
7,650
|
20,000
|
CHD among Younger Participants
|
|
CHD
|
Total
|
|
Yes
|
No
|
|
Bald
|
25
|
2,475
|
2,500
|
|
Hairy
|
90
|
8,910
|
9,000
|
|
Total
|
115
|
11,385
|
11,500
|
a. Calculate the risk of CHD in the older men. Calculate the risk of CHD in the younger men. Does there appear to be an association between age and CHD? Why or why not?
b. What proportion of the older men are bald? What proportion of the younger men are bald? Does there appear to be an association between age and baldness?
c. Based on your answers to Questions 4a and 4b, does the association between baldness and CHD appear to be confounded by age? Why or why not?
d. Calculate the relative risk of CHD associated with baldness in the stratum of older men. Briefly explain how to interpret the value you calculated.
e. Calculate the relative risk of CHD in the stratum of younger men. Briefly explain how to interpret the value you calculated.
f. Compare the relative risks in Questions 4d and 4e with each other and with the overall relative risk you calculated in Question 3c. Do these results suggest that the association between baldness and CHD is confounded by age? Why or why not?