In a study related to the effectiveness of e text books in the classroom college students were broken into two groups. The first was given a traditional text book while the second group was provided an e text only. At the end of a semester long statistics course the overall grades of the students were collected.

Final Grade

Group 1 (Traditional text)

49, 67, 69, 72, 74, 78, 82, 82, 85, 88, 91, 93

Group 2 ( e -text)

55, 61, 70, 75, 78, 85, 89, 90, 93, 95, 99

Which of the following would you recommend the researcher consider when setting up the test to ensure the results were as accurate as possible ?