9.55 Paired-samples t test, decorations in kindergarten classrooms, and science learning: Psychology researcher Anna Fisher and her colleagues studied whether kindergarten students learned better in decorated classrooms or undecorated classrooms, referred to as “sparse classrooms” (Fisher et al., 2014). They wondered whether students would be less distracted and learn better without decorations such as posters, maps, and children’s artwork. The same group of children had science lessons in a classroom without decorations and in a classroom with decorations. The students took a test on the material after each condition. Each child received a percentage-correct score, out of 100%, for each condition. In the journal article in which they reported their findings, the researchers wrote that the children’s “learning scores were higher in the sparse-classroom condition (M = 55%) than in the decorated-classroom condition (M = 42%),

paired-samples t(22) = 2.95, p = .007; this effect was of medium size, Cohen’s d = 0.65.”

a. What is the independent variable in this study and what are its levels?

b. What is the dependent variable in this study?

c. Why did the researchers analyze their data with a pairedsamples t test?

d. How many children participated in this study? Explain how you determined your answer.

e. How do you know this result is statistically significant?

f. Using the means, explain the results to someone who has not taken statistics. g. Why did the researchers report an effect size?