13.13 Writing about testing worries and exam performance. For many students, self-induced worries and pressure to perform well on exams cause them to perform below their ability. This is because these worries compete with the working memory available for performance. Expressive writing has been shown to be an effective technique to overcome traumatic or emotional experiences. Thus, a group of researchers decided to investigate whether expressive writing prior to test-taking may help performance.⁹

The small study involved 20 subjects. Half the subjects were assigned to the expressive-writing group and the others to a control group. Each subject took two short mathematics exams. Prior to the first exam, students were told just to perform their best. Prior to the second exam, students were told that they each had been paired with another student and if the members of a pair both performed well on the exam, the pair would receive a monetary reward. Each student was then told privately that his or her partner had already scored well. This was done to create a high-stakes testing environment for the second exam. Those in the control group sat quietly for 10 minutes prior to taking the second exam. Those in the expressive-writing group had 10 minutes to write about their thoughts and feelings regarding the exam. The following table summarizes the test results (% correct):

FIGURE 13.8 Interaction plot, Exercise 13.12.

	First exam		Second exam
Group		s		s
Control	83.4	11.5	70.1	14.3
Expressive-writing	86.2	6.3	90.1	5.8

(a) Explain why this is a repeated-measures design and not a standard two-way ANOVA design.
(b) Generate a plot to look at changes in score across time and across group. Describe what you see in terms of the main effects and interaction.
(c) Because exam scores can run only between 0% and 100%, variances for populations with means near 0% or 100% may be smaller and the distribution of scores may be skewed. Does it appear reasonable here to pool variances? Explain your answer.