ANOVA Between Subjects Flashcards
Why can’t multiple t tests be used to determine a difference between multiple means?
As number of comparisons increases, so does type 1 error probability
What is the formula for familywise error rate?
a_FW= ca’
What does ANOVA compare?
The size of the difference (variance) within groups compared to the size of the differences between groups.
What is the logic of statistical testing?
Observed differences relative to expected differences. (Our data - value under null, in proportion to (divided by) expected difference under the null)
What can between groups variability be due to? 3
Treatment effect/levels of factor Individual differences Experimental error
What can within groups variability be due to? And not due to?
Individual differences and experimental error NOT treatment effect
What are mean squares?
Unbiased estimate of population variance (based on df)
If the null is true, F values will be around __ ?
1
Why is the F distribution always positive?
Variances cant be negative because they are squared values
Do F tests provide directional tests?
No
What is SS_total?
Summed squares of each scores’ deviation from grand mean.
How many values are used to calculate SStreatment?
Number of group means minus one
How do you know which critical value is more conservative if there is no precise one on the table?
The higher critical value if trying to exceed it. (Smaller df for ANOVA)
What does and doesn’t ANOVA tell us?
Whether the means are different; which one is different
What is the df for SSerror?
The sum of N-1 for all groups; or N-k for equal size groups
