Instead of investigating the chance of going 18 months without a root canal your practice is only interested in the chance of having a root canal given various exposures, so you decide to do case-control study.

Suppose that for every root canal case from the previous 18 months, 3 controls were selected and both cases (43) and controls (129) were asked the about various exposures.

1. Fill in the exposure odds and ORs for all the exposures in the table below (counts in the table are for those patients who had the exposure). For each OR use the odds of having the particular exposure in cases compared to controls. (9 pts)IN PREP

exposure	Cases(odds)	Controls (odds)	OR
Have gum disease	15	10
Chew sugarless gum	6	20
Floss regularly	10	65
Taken antibiotics in previous 6 months	5	35
Overweight/obese	20	38
Recent viral infection	17	51

1. Which of these exposures appear protective and which appear harmful? (3 pts)

1. What doesn't appear to have any association? (1pt)

1. If the controls are a random selection of anyone who did not have a filling in a molar vs. those who did, how might that impact the ORs?(2pts)

1. If ALL participants were patients who also had a molar filling is the OR a good estimate of the RR? Why or why not? (2 pts)

1. Discuss both 1 strength and 1 weakness of using a case-control here (assume they used anyone with a root canal in this practice the last 18 month as cases and any patient from this practice who did not as controls and controls are the same ages as cases) (3 pts)