ANOVA Flashcards
What are the steps to perform an ANOVA?
- Calculate between group variance
- Calculate within group variation
- Calculate the mean squares
- Calculate F statistics
- Compare F statistics with critical value
- Eta Squared
What does ANOVA compare?
variation between groups against the variation within groups
When should ANOVA be used?
3 or more samples (advantage over t test)
Nominal and interval/ration varianbles
What does ANOVA investigate?
how much of this total variance has to do with differences the researched variable, and how much has to do with other factors.
When is the null hypothesis rejected?
If there are wider variations BETWEEN groups than within each group
How is degrees of freedom calculated BETWEEN groups?
DF = k -1
K = number of groups/samples
How is degrees of freedom calculated WITHIN groups?
DF = K(n-1)
K = number of groups/samples
n = number of cases in that group
What is the F statistics?
a. The F-statistic compares the two mean squares by computing the ratio of the mean of squares between and the mean of squares within
e. g SSBetween / SSWithin = F statistic
When is the F statistics significant? (reject null)
If our score is greater than the critical value
Why would the F statistics be larger?
When there is a greater difference between groups than within groups
How do you find the critical value?
F statistics Critical values Table
- Column: Larger SS and its DF
- Row: DF of smaller SS
What is does the eta squared measure?
What proportion of all variance is explainable by between-group variance”?
What is the statistical term from measuring the effect of size?
Eta Squared
How do you caluculate eta squared?
SSbetween / SSTotal
SStotal = SSbetween+SSWithin
