Coffee drinkers are often smokers, so the data from the case-control study were stratified by smoking, as shown below:

Average Coffee Consumption	Never Smokers		Ever Smokers
	Cases	Controls	Cases	Controls	Total
5 cups	27	114	175	25	341
< 5 cups	31	76	67	85	259
Total	58	190	242	110	600

1. Compute the OR for the association between average coffee consumption and liver cancer in never smokers and ever smokers:

Coffee drinkers are often smokers, so the data from the case-control study were stratified by smoking, as shown below:

Average Coffee Consumption	Never Smokers		Ever Smokers
	Cases	Controls	Cases	Controls	Total
5 cups	27	114	175	25	341
< 5 cups	31	76	67	85	259
Total	58	190	242	110	600

2. Is smoking a confounder, an effect modifier, or neither? Explain why.

3. If appropriate, calculate the Mantel-Haenszel odds ratio. If it is not appropriate to calculate the Mantel-Haenszel odds ratio in this situation, what would you report?

4. What are the potential sources of bias in this investigation?

5. If cases and controls were misclassified according to their exposure status (coffee drinking), but misclassification was similar among cases and controls, what is the effect on the odds ratio?

6. Suppose misclassification was not similar among cases and controls (for example, if cases were more likely to report coffee consumption as compared to controls), what is the effect on the odds ratio?