Chapter 4: Q. 70 (page 265)

Diet soda and pregnancy A large study of $3000$ Canadian children and their mothers found that the children of mothers who drank diet soda daily during pregnancy were twice as likely to be overweight at age $1$ than children of mothers who avoided diet soda during pregnancy.
a. A newspaper article about this study had the headline “Diet soda, pregnancy: Mix may fuel childhood obesity.” This headline suggests that there is a cause- and-effect relationship between diet soda consumption during pregnancy and the weight of the children $1$ year after birth. However, this relationship could be explained by other variables. What other variables might be confounded with a mother’s consumption of diet soda during pregnancy?
b. You have $300$ pregnant mothers who are willing to serve as subjects in an experiment that compares three treatments during pregnancy: no diet soda, one diet soda per day, and two diet sodas per day. Write a few sentences describing a completely randomized design for this experiment.

Short Answer

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(a) The other variables that are confounding are the condition of the mother during pregnancy, the food they are eating, and also the immune system of mother and child.

(b) There are various ways to randomize the mothers for comparing them to having one diet soda per day, having two diet sodas per day, or having no diet soda at all, like it can be divided into three.

Step by step solution

Part (a) Step 1: Given Information

We are given the experiment about pregnant mothers' having diet soda and not having diet soda, and we have to find out the other variables confounding the mothers' pregnancy.

Part (a) Step 2: Explanation

There are two variables that can be confounded during the experiment. Soda can increase or decrease the weight of the baby, but aside from this, there are other variables that can affect the baby's weight, like the food eaten by the mother during pregnancy and also the condition of mother during pregnancy, like the immune system.

Part (b) Step 1: Given Information

We are given the experiment about pregnant mothers' having diet soda and not having diet soda, and we have to find out the way for working of randomization in the mothers.

Part (b) Step 2: Explanation

According to the question, three hundred mothers are available, and the mothers should be randomized in such a way that one hundred students should have no diet soda, and the other one hundred should have one diet soda per day, and the remaining one hundred should have two diet sodas per day. There are many other ways to randomize.