Analysis of Variance (ANOVA)
ANOVA data Grand Mean = 4.375 Control Placebo Drug 5 6 2 8 3 4 1 7 10 1 7 10 Mean = 6.5 Mean = 4.5 Mean = 2.125 Grand Mean = 4.375
Independent t-test
Variance
ANOVA data Grand Mean = 4.375 Control Placebo Drug 5 6 2 8 3 4 1 7 10 1 7 10 Mean = 6.5 Mean = 4.5 Mean = 2.125 Grand Mean = 4.375
Variance total variance = within groups variance + between groups variance
May Affect Number of Headaches genetics stress diet gender sleep … new drug Error --- IV
ANOVA data IV (drug) error Control Placebo Drug 5 6 2 8 3 4 1 7 10 1 7 10 Mean = 6.5 Mean = 4.5 Mean = 2.125 IV (drug) error
Between-group var = IV + error Within-group var = error F = between var / within var = (IV+error) / error If IV has no effect, F = error/error = 1 Is F significantly greater than 1?