Solved – Why did I get significant difference result before using post-hoc test but I got an insignificant result after using post-hoc test


I have done an one-way anova test for to compare among 4 groups. I did the homogeneity test for variance and the result showed the variance was not equal but there was a significant difference between group (p=0.013). Thus, I did the Dunnett's T3 test for post-hoc test. However, the p values between all the groups were more than 0.05. How would this happened? Does it mean there are no significant difference between the 4 groups?

Thank you for answering my question.

Best Answer

Be careful not to interpret ANOVA as a test of whether there is at least one different group among the bunch. It is a test with the null hypothesis that the between group variance is 0. A significant result doesn't guarantee some group will deviate significantly from some other group.