Leah is a psychologist interested in whether the mental process of reading an e-book is different from reading a printed book.
She randomly sorts 40 volunteers into two groups. The 20 volunteers in one group read an e-book. The other 20 read a paperback copy of the same book. Afterward, each volunteer completes a reading comprehension test and Leah records their scores.
Scores for people who read the e-book
1353181104703101584369
Mean: 4.6 points
Scores for people who read the paperback book
10109748610286430484478
Mean: 6.1 points
How much lower is the average for the treatment group than the average for the control