Question

What is a post-hoc test and why is it necessary to use one after a significant ANOVA?

Answer #1

Post-hoc test is a test which is use to test the significance of the difference of the means of two groups ( treatments means) simultaneously when the ANOVA test is significance.

It is necessary because of the following region.

If the level of significance is = 0.05

And suppose there are five groups.

Suppose ANOVA test is significance then we want to test difference of the means of the groups using two sample test using the level of significance = = 0.05.

We need to total test = 4 + 3 + 2 + 1 = 10

So level of significance become 1 - ( 1 - )^10 =1 - (1- 0.05)^10 = 1 - 0.5987 = 0.4013

Which is very large.

So we need to use Post-hoc test, it use 0.05 level of significance to compare all the pairs simultaneously.

Explain when and why a post hoc test test is necessary after
conducting one-way analysis of variance.

Week 8 Discussion
Consider the different post hoc tests discussed in the readings
and respond to the following:
Describe the general rationale behind using post hoc tests
(i.e., when they are used and why).
One of the advantages of using an ANOVA (compared to using
t-tests) is also a disadvantage—using an ANOVA makes it
necessary to use post hoc tests if there is a significant main
effect. We use a post hoc test because there is one specific
advantage in...

What is a post hoc test and why is this test applied in
research?

12. What is the total of the ANOVA split into?
16. What is a post hoc test and why don’t you need it if your
ANOVA is not significant?
18. What happens to the curve as the degrees of freedom for the
numerator and for the denominator get larger? This information was
also discussed in previous chapters.

1. What are the differences between planned contrasts (or
planned comparisons) and post hoc tests? Why are they used after
performing a one-way ANOVA? How do you decide which to use of the
two types of follow-up tests?
2. What are the main differences between between- and
within-groups one-way ANOVAs? What determines which type of test
should be used? Which is a stronger test and why?

What is the purpose of doing a post-hoc
test?

Explain why post-hoc tests are needed for an ANOVA, and whether
it would or would not be conducted if the decision from the ANOVA
was to fail to reject the null hypothesis.

State whether a post hoc test is necessary for each of the
following results. Explain your answer for each result.
a.) F(1,18)=6.29, p<0.05
b.) F(4,55)=3.98, p<0.05
c.) F(2,33)=2.03, p>0.05

The post-hoc analysis Tukey’s HSD test is the appropriate type
of post-hoc analysis whether the number of scores per group is the
same or whether there are a different number of scores in each of
the group.
True
False

An ANOVA is as an Omnibus test. Briefly describe what this
means, and also indicate why post-hoc tests are important.

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