Answer:
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.
