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.