In a study of breast cancer, a mother was considered exposed if she first gave birth at 30 years of age or older. among 1,628 mothers who were exposed, 31 subsequently developed breast cancer. among the 4,450 mothers who first gave birth before the age of 30, 65 subsequently developed breast cancer. what is the result for the appropriate measure to describe the strength of the association between age at first birth and breast cancer?

The theory says that one exposed mother is the one that gave birth after the 30s.

from 1628 exposed ones, 31 developed breast cancer, this means that a:

31/1628*100% = 1.9%

1.9% of the exposed sample developed cancer.

For the other part, of 4450 ones that weren't exposed, 65 developed cancer, the percent is:

65/4450*100% = 1.46%

So we can see that the ratio is smaller with the non-exposed ones.

The strength of the association can be calculated as:

(31/1628)/(65/4450) = 1.3

Meaning that an exposed person is 1.3 times more likely to develop cancer.