Part B: You are interested in exploring if the mother’s alcohol drinking status
ID: 78897 • Letter: P
Question
Part B:
You are interested in exploring if the mother’s alcohol drinking status during pregnancy is a confounder and/or an effect modifier. Using the two tables below, calculate the stratum specific relative risks for women who drank during pregnancy versus women who did not drink during pregnancy.
4. From the table below, calculate the stratum specific relative risk for female babies whose mothers drank Blank 4
Mothers Who Drank During Pregnancy
Low Birth Weight
Normal Birth Weight
Total
Female Babies
73
51
124
Male Babies
21
62
83
Total
94
113
207
5. From the table below, calculate the stratum specific relative risk for female babies whose mothers did not drink Blank 5
Mothers Who Did NOT Drink During Pregnancy
Low Birth Weight
Normal Birth Weight
Total
Female Babies
31
121
152
Male Babies
19
129
148
Total
50
250
300
6. Is drinking status during pregnancy a confounder? YES or NO (all capitalized) Blank 6
7. Is drinking status during pregnancy an effect modifier? YES or NO (all capitalized Blank 7
Mothers Who Drank During Pregnancy
Low Birth Weight
Normal Birth Weight
Total
Female Babies
73
51
124
Male Babies
21
62
83
Total
94
113
207
Explanation / Answer
Low birth weight is considered as risk group/disease group here.
The stratum-specific risk ratios are as follows:
4)
For female babies whose mothers drank
(73/124) /(21/83) = 0.5887096774/0.2530120481 = 2.32680491629
5)
For female babies whose mothers did not drink
(31/152)/(19/148) = 0.2039473684/ 0.12837837837 = 1.58864265922
6)
Yes.
Gender and alcohol seems to have confounded the observations. Sex of fetus is not dependent on alcohol. It depends on which sperm fertilizes the egg. If it is happening randomly, we see males and females in 1:1 ratio. It is true for non-alcoholic mothers (152:148). But in alcoholic mothers, it is different (124:83). Alcoholic mothers produced more female children than males.
7)
Yes.
Effect modification occurs when an exposure has a different effect among different subgroups.
2.33 is clearly more than 1.6