Question: A case control study was done to investigate the association between tuberculosis and heavy smoking in a particular population. One question that arose was whether or not there was an interaction between age and smoking with respect to tuberculosis - that is, does the risk of tuberculosis due to smoking increase in older patients? The following data are available:

a) What is the association between smoking and tuberculosis among those aged 39 or less? What is the association between smoking and tuberculosis among those aged 50 or more?

b) Is there a significant difference between the two age groups with respect to the association between smoking and tuberculosis? Justify your answer.