Answer (a) — incorrect: You must compare the crude and adjusted OR's to evaluate confounding. Remember, the crude estimate simply reflects the association between the exposure and outcome; it does not take into account the effect of potential confounders.

Answer (b) — incorrect: You must compare the crude and adjusted OR's to evaluate confounding. Remember, the adjusted estimate simply reflects the association between the exposure and outcome after controlling for a potential confounder. Without the crude to compare back to, we would not know what happened to the OR after taking other risk factors into account.

Answer (c) — correct: It is important to compare the adjusted OR with the crude OR to see the change in the effect estimate. To evaluate the magnitude of confounding, the rule of thumb is to look at the percent change in the adjusted estimate. If the adjusted estimate differs from the crude by 10% or more, then it is customary to consider that variable as a confounder. The adjusted odds ratio is reported to describe the exposure-disease association controlling for the confounder.