The article "Yes That Miley Cyrus Biography Helps Learning" (The Globe and Mail, August 5, 2010) describes an experiment investigating whether providing summer reading books to low-income children would affect school performance. Subjects in the experiment were 1330 children randomly selected from first and second graders at low-income schools in Florida. A group of 852 of these children were selected at random from the group of 1330 participants to be in the "book" group. The other 478 children were assigned to the control group. Children in the book group were invited to a book fair in the spring to choose any 12 reading books which they could then take home. Children in the control group were not given any reading books but were given some activity and puzzle books. This process was repeated each year for 3 years until the children reached third and fourth grade. The researchers then compared reading test scores of the two groups.
a. Explain why randomly selecting 852 of the 1330 children to be in the book group is equivalent to random assignment of the children to the two experimental groups.
b. Explain the purpose of including a control group in this experiment.