A pediatrician is conducting an experiment to determine which brand of baby food (A, B, or C) and amount of tummy time (half an hour a day or none) will produce healthier babies, determined by weight gain in the first few months after starting the baby food. Her patients are divided into equally sized groups and are randomly assigned to a brand of baby food and amount of tummy time. In this experiment the subjects were randomly assigned to the different treatments. What is the most important reason for this random assignment? A. Random assignment reduces the amount of variation in baby weights.
B. Random assignment makes it possible to make a conclusion about all babies.
C. Random assignment prevents the placebo effect from ruining the results of the study.
D. Random assignment eliminates the effects of other variables such as parental involvement and socioeconomic class.
E. Random assignment is a good way to create groups of subjects that are roughly equivalent at the beginning of the experiment.