Question

A study looking at ovarian cancer in women compared cases with non-cases, and found that 150/200 cases did not use birth control compared with 50/200 of the non-cases.

1) Create a table to display the data.

2) Calculate the odds of exposure in cases and non-cases.

3) Calculate the odds ratio using the cross-product ratio.

4) How does the difference between the two prevalences of ovarian cancer (75% vs 25%) compare to the odds ratio?

Answer 1

Answer 1 :)

Subjects	Exposed	Unexposed	Total
Cases	150	50	200
Non Cases	50	150	200
Total	200	200	400

Answer 2 :)

Odds of Exposure in the case= Exposed/Unexposed

Odds of Exposure in the case = 150/50

Odds of Exposure in case = 3

Odds of Exposure in the non-case= Exposed/Unexposed

Odds of Exposure in the non-case = 50/150

Odds of Exposure in the non-case = 0.3

Answer 3 :)

Odds ratio = Odds of Exposure in the case /Odds of Exposure in the non-case

Odds ratio = 3 /0.3

Odds ratio = 10:1

Answer 4:)

The ratio of the two prevalence of ovarian cancer = 75% / 25%

The ratio of the two prevalence of ovarian cancer = 3

The prevalence ratio is 3:1 while the odds ratio is 10:1. It suggests that the prevalence does not provide sufficient evidence of the severity of the disease while the odds ratio is suggesting the risk factor associated with the cases.

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