Question

Researchers at Johns Hopkins decide to use a case control study design to explore the association between women with breast cancer and DDT exposure. They interview women that have breast cancer undergoing chemo at the Johns Hopkins Hospital in Baltimore in 2014 and then take blood samples to test for DDT exposure. They also enroll a group of controls (without breast cancer) in the study based on patient lists at the hospital and also test them for DDT exposure. They find that that 360 of the women with breast cancer have DDT, exposure while 1,079 do not. Among the controls 432 have DDT exposure, and 2,446 do not.

A. Create an appropriate 2x2 table for this data.

	Breast Cancer (Cases)	No Breast Cancer (Controls)
DDT EXPOSURE	360	432
NO DDT EXPOSURE	1,079	2,446

B. Calculate the odds ratio comparing the odds of exposure for those with breast cancer to the odds of exposure for those without breast cancer (show work please)

C. Assume that this OR is significant. What does this OR mean (be specific using the context of this study)?

Answer 1

Result:

Researchers at Johns Hopkins decide to use a case control study design to explore the association between women with breast cancer and DDT exposure. They interview women that have breast cancer undergoing chemo at the Johns Hopkins Hospital in Baltimore in 2014 and then take blood samples to test for DDT exposure. They also enroll a group of controls (without breast cancer) in the study based on patient lists at the hospital and also test them for DDT exposure. They find that that 360 of the women with breast cancer have DDT, exposure while 1,079 do not. Among the controls 432 have DDT exposure, and 2,446 do not.

A. Create an appropriate 2x2 table for this data.

	Breast Cancer (Cases)	No Breast Cancer (Controls)
DDT EXPOSURE	360	432
NO DDT EXPOSURE	1,079	2,446

B. Calculate the odds ratio comparing the odds of exposure for those with breast cancer to the odds of exposure for those without breast cancer (show work please)

For cancer: people who exposure / people who did not = 360/1079

People who No cancer people who exposure / people who did not = 432/2446

Dividing the two results, we get (360/1079) / (432/2446) = 1.889

Odds ratio= 1.889

C. Assume that this OR is significant. What does this OR mean (be specific using the context of this study)?

The odds are 1.889 times higher ( or 88.9% more than) that a person with DDT exposure will get the Breast Cancer compared to a person without DDT exposure.