2. A 1970s study of oral contraceptives (birth control pills) gathered data on t
ID: 3073191 • Letter: 2
Question
2. A 1970s study of oral contraceptives (birth control pills) gathered data on thousands of women. Among other things, the researchers recorded each woman's blood pressure and how many children she had. The study showed that if you compared blood pressures for with two children and women with four children, the average for those with four c was about 30 points higher than for those with only two. The careless conclusion is that ing children causes your blood pressure to go up. Actually, though, selection bias is at wo Mothers in the first group (two children) tend to be than mothers s second group, and as you get this data set, number of children is confounded with women t hav ork , your blood pressure tends to go up. So forExplanation / Answer
The answers for the three blanks are:
A 1970s study.....to go up. Actually, though, selection bias is at work. Mothers in the first group(two children) tend to be younger than mothers in the second group, and as you get older , your blood pressure tends to go up. So for this data set, number of children is confounded with age.
EXPLANATION
We would expect the women with four children to be (on average) older than the women with two children. Thus, if we compare the blood pressures of these two groups, we need to take into account the effect of age as well since the blood pressure increases with age.
Thus, in this study age acts as a confounding variable, and the number of children is confounded with age.
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