A new type of soy-based baby formula has been developed to help babies who have trouble gaining weight in their first six months of life. The parents of 150 babies have volunteered their children to participate in this study. All of the babies are between 8 and 9 weeks of age (a time when they should be growing very rapidly) and have been identified by their doctors as gaining weight more slowly than normal. The babies will be weighed before the study begins. Half of them will be given the new formula and the other half will be given the type of formula that is currently recommended for slowly growing babies. After three months, all the babies will be weighed again. a) Describe an appropriate method for assigning the subjects to the two groups so that each group will have an equal number of subjects.
b) In this study, the researchers chose to include a group who used the currently recommended brand of formula. Why is it important to include a control group in this study even though weights will be measured at the beginning and at the end of the study?
c) Many babies continue to drink formula until they are 12 to 15 months of age. Why would the researchers choose to use only babies who are about 2 months old (about 8 to 9 weeks old) in the study?