About
To compare the gain scores across all groups, use anova
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Steps
Homogeneity of variance assumption
First, check the homogeneity of variance assumption:
leveneTest(data$score, data$condition, center="mean")
Levene's Test for Homogeneity of Variance (center = "mean")
Df F value Pr(>F)
group 3 1.1269 0.3436
76
leveneTest(data$score, data$condition)
Levene's Test for Homogeneity of Variance (center = median)
Df F value Pr(>F)
group 3 1.3134 0.2763
76
Anova
aov.model = aov(data$score ~ data$condition)
summary(aov.model)
Model comparison
anova(model1, model2)