In a small cohort study investigating the effect of a rare exposure ( E), the following results were found:
Table 1 Disease
| Yes
|
No | |
| Yes | 120
|
360 |
| No | 120
|
360 |
Exposure
- Is there an association between exposure and disease? Show the way you reached the conclusion. [2 points]
- A stratified analysis by Age-groups shows the following:
|
|
Younger adults | Older adults | |||
| Disease | Disease | ||||
| Exposure |
Yes |
No |
Exposure | Yes | No |
| Yes
|
60 | 180 | Yes | 80 | 160 |
| No
|
40 | 160 | No | 60 | 180 |
What is the relative risk (RR) of exposure causing disease in younger adults and what is the RR in older adults? [ 4 points]
c- How do you explain this result? (No more than 60 words) [4 points]
(it is recommended to use the supplementary reading by (8 points)
- a) Give one example of typical bias for a cohort study and explain why it creates a bias (no more than 100 words) [4 marks]
- b) Give one example of typical bias for a case – control study and explain why it creates a bias (no more than 100 words) [4 marks]
Q 5 A cohort study was conducted to examine cigarette smoking and the risk of oral cancer. The investigators selected exposed and unexposed subjects so that they had exactly the same distribution of race. This method to address confounding by race is called: (2 points)
- Restriction
- Stratification
iii. Matching
- Multivariate analysis
- None of the above
Question 6:
A study aims to determine the incidence of type 2 diabetes. A cohort of 200 people age 65 years or older who were initially disease –free participated in the study. One hundred and fifty people were examined at the end of 3 years. Fifty other participants from the initial cohort could not be examined, including 11 people who had died. Does this loss of participants represent a source of bias? Justify your answer. [4 points] no more than 80 word
