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Part 3: Association Study


 

 

One way to help select which gene to target is by doing an association study.  The type of association study that you will be using is a case-control study. 

To analyze a case-control study you will calculate an odds ratio from the case and control genotypes.  The odds ratio is a measure of the strength of the association between the disease and a risk (or protective) factor. An example is shown below:

 

Cases

Controls

Risk factor

a

b

No risk factor

c

d

Odds ratio = ad/bc

 

Lung Cancer Cases

                Controls

Smoker

38

467

Non-smoker

47

1500

Odds ratio = (38*1500)/(47*467) = 2.60

95% Confidence Interval = 1.67 4.03

The confidence interval, or range of plausible results given this sample size and data, has been calculated for you.  In this instance, smoking has a confidence interval above 1.  It is a significant risk factor for lung cancer. This indicates that patients with lung cancer were more likely to have been smokers.  If the confidence interval had been below 1, it would be a significant protective factor.

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