Omnibus F

An omnibus F is an F ratio (the calculated statistic from an ANOVA Table) that shows that there is a definite significance somewhere between the treatment groups.

AKA: significant F, overall F

*Note: Whenever the omnibus F is significant, we know that the treatment or variable of interest is effective (a difference between the groups is highly probable). At least two of the groups are significantly different (usually the two groups that are the most different), but we don`t know for sure which pair(s) are.

If the F test is non-significant, we conclude that the treatment was not significant and we have insufficient evidence to rule out chance for the differences between the group means. Although we are willing to assert that there is no real difference between all of the gropus` means, we may be in error since the omnibus F test is testing the average difference between all of the means.  However, if we had a hypothesis that one of the group`s mean is significantly different from another group`s mean and used a single planned comparison between the two, we would likely have come up with proof of significance. 

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