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O A post-hoc test is needed after we complete an ANOVA in order to determine which groups differ from each other. o Do not conduct a post-hoc test unless.

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Presentation on theme: "O A post-hoc test is needed after we complete an ANOVA in order to determine which groups differ from each other. o Do not conduct a post-hoc test unless."— Presentation transcript:

1 o A post-hoc test is needed after we complete an ANOVA in order to determine which groups differ from each other. o Do not conduct a post-hoc test unless you found an effect (rejected the null) in the ANOVA problem. If you fail to reject the null, then there are no differences to find. Post HOC Testing

2 Effect of drug doses on AST activity 12345 2329383031 2725312733 263328 31 1936352228 303233 30 28363424 2730353429 2531373230 SourceSSdfMSF cal. Between groups276.25469.065.76 Within groups (residual)419.753512.00 Total696.0039 ANOVA Table F cal (5.76) > F tab (2.64)

3 Tukey’s HSD (Honestly significance difference) Post-hoc test The critical value for comparison between two averages Sample size /group Number of groups = number of means = r Total sample size (for all groups) Number of groups = number of means = r Number of groups Critical q value (tabulated)tabulated (0.05, 0.01) N – g = df of the WITHIN MS

4 Effect of drug doses on AST activity 12345 2329383031 2725312733 263328 31 1936352228 303233 30 28363424 2730353429 2531373230 n88888 Sum207244273240236 Mean28.7530.534.133029.5 Variance (s)13.2611.1410.9817.437.14 g = 5 Df within = N - g = 35 SourceSSdfMSF cal. Between groups276.25469.065.76 Within groups (residual)419.753512.00 Total696.0039 MS within = 12

5 q(5, 35, 0.05) = 4.07Within MS = 12n /group= 8 x3 - x1 = 8.26 > 4.96; x3 - x5 = 4.63 < 4.96; x2 - x1 = 4.63 < 4.96 Significant Not significant and so on.


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