You conducted a series of observational studies looking for an association betwe

Question

You conducted a series of observational studies looking for an association between exposure to second hand smoke and childhood asthma.

a) First you conducted a cross-sectional study. Your prevalence odds ratio is 8.2. Interpret this outcome.

b) Next you conducted a case-control study with a resulting odds ratio of 10.4. Interpret this outcome.

c) With the results from the first two studies, you were able to get funding for a cohort study. At the end of the 25 year study, your risk ratio was 9.8. Provide an interpretation for this outcome.

Explanation / Answer

(a) In cross-sectional study, the researcher collects data from the entire population in a definite time point or time duration. So the subjects in this study are coming randomly from the entire population of human. Everybody is asked two questions and depending on yes/no they belongs to the frequency of the four cells in the 2x2 contingency table.

The odds ratio is 8.2. That means the odds of having childhood asthma is 8.2 times for those who were exposed to second hand smoking than those who are not exposed to second hand smoking in the entire population.

(b) In case-control study the researcher uses a certain characteristic for the sample. Cases are those who have the disease or characteristic and control groups are samples from those who do not have the disease. Each group is asked one question: Exposed to second hand smoke or not?

The odds ratio is 10.4, that means odds of being diseased or having childhood asthma is 10.4 times higher for those who have been exposed to second hand smoking than those who have not.

(c) Cohort study is a large longitudinal study which gives the researcher scope to compute the probability of developing the disease.

The risk ratio is 9.8, that means the probability of having childhood asthma is 9.8 times higher for those who have been exposed to second hand smoking than who have not.

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