1. The teacher noticed that some students reported feeling more motivated when revising in groups. She decided to conduct an experiment to compare group revision and solo revision.

Twenty A Level psychology students from the school took part in the study. They were randomly allocated to one of two conditions:

• Condition A: revise alone for 15 minutes

• Condition B: revise in groups of 3 or 4 for 15 minutes

All students revised the same set of psychology terms. After the revision period, all students completed a 20-mark test on the material. The teacher recorded each student’s score.

Explain one way in which the experiment could be changed to control the problem of using different participants in each condition.