What does the F-ratio in ANOVA represent?

• A. Between-group variance divided by within-group variance
• B. Within-group variance divided by between-group variance
• C. Total variance divided by error variance
• D. Variance of means across groups

Answer: (A)

ANOVA uses the F-ratio to compare two sources of variability: signal (differences between group means) and noise (random variation within groups). The numerator measures how far the group means are from the overall mean (between-group variance), while the denominator measures how much observations vary inside each group around their own mean (within-group variance). The F-ratio, calculated as MS_between divided by MS_within, tells us how large the between-group variation is relative to the within-group variation. If there are no real differences between groups, these variances are similar and the F value stays near 1. If real differences exist, the between-group variance becomes larger relative to the within-group variance, pushing F upward and providing evidence against the null hypothesis.