# Case-Control Study OR Export

Source conversation: Case-Control Study OR

## Recognize the study design

This is a case-control outbreak investigation, so the association measure is the odds ratio rather than the risk ratio.

The exercise uses 26 cases and 26 controls from the same hotel population and asks for one 2 x 2 table per food eaten at lunch.

Formula:

OR = (a d) / (b c)

where a and b are exposed and unexposed cases, while c and d are exposed and unexposed controls.

## Calculate each food odds ratio

| Food | Cases ate | Cases did not eat | Controls ate | Controls did not eat | Odds ratio |
| --- | ---: | ---: | ---: | ---: | ---: |
| Pasta with meat sauce | 25 | 1 | 18 | 8 | 11.11 |
| Grilled steak | 23 | 3 | 18 | 8 | 3.41 |
| Russian salad | 10 | 16 | 5 | 21 | 2.63 |
| Tiramisu | 7 | 19 | 3 | 23 | 2.82 |

Example for pasta with meat sauce:

OR = (25 x 8) / (1 x 18) = 200 / 18 = 11.11

## Write the submission-ready conclusion

Pasta with meat sauce has the highest odds ratio. Its OR is about 11.11, meaning the odds of having eaten it were about 11 times higher in cases than in controls.

Therefore, pasta with meat sauce is the food most strongly associated with the outbreak and is the most likely vehicle of infection.

Very short final version:

Because this is a case-control study, I constructed a 2 x 2 table for each food and calculated the odds ratio. Pasta with meat sauce had the highest odds ratio, so it is the most likely source of the outbreak.