Development of Asthma
A study was conducted to evaluate the relationship between exposure to second hand smoke at early age and the development of asthma. In the study, 1000 infants who were exposed to second hand smoke before 4 months of age are compared to 1000 infants who not been exposed to second hand smoke. These infants were followed for 10 years to assess the status of asthma. The results are shown in table below.
Relationship between exposure to second hand smoke at an early age and development of asthma.
| Introduction of solid food | Health status | ||
| Asthma | No Asthma | Total | |
| Exposed | 200 | 800 | 1000 |
| None Exposed | 100 | 900 | 1000 |
| Total | 300 | 1700 | 2000 |
1. What is the risk of asthma in the group that had been exposed to second hand smoke?
2. What is the risk of asthma in the group that had not been exposed to second hand smoke?
We have conducted another hypothetical study of the relationship of smoking to coronary heart disease (CHD). We identified 9,000 adults free of CHD at the beginning of the study. During the 20-year follow-up period 94 smokers had developed CHD and 97 non-smokers had developed CHD.
3. What is the exposure in this study? _____________
4. What is the outcome in this study? _____________
5. What is the study design?
Answer the following questions
6. What is a Case-control study and what are its strength and weakness?
7. What is a Cohort study and what are its strength and weakness?