Within-subjects Anova

Question 1

What is a Within-subjects Anova?

Answer 1

analyzing the differences between
3 or morelevels of IV
where all P have taken part in all conditions.

has to be equal (variance)

Question 2

What is sphericity?

Answer 2

the condition where the variances of the differences between all combinations of related groups (levels) are equal.

Question 2

How to calculate a one-way within-subjects ANOVA

Answer 2

Collect Data:

State Hypotheses:

Calculate Group Means:
Compute the mean for each group (condition or time point) and the overall mean.

Calculate Within-Groups Variability (SSW):
Calculate the sum of squares within groups

Calculate Between-Groups Variability (SSB):
Calculate the sum of squares between groups

Calculate Total Variability (SST):
Calculate the total sum of squares

Degrees of Freedom (df)

Calculate Mean Squares

Calculate F-Statistic

Compare F-Statistic with Critical Value

Determine the critical F-value for your chosen significance level (e.g., α = 0.05) and degrees of freedom.

Interpret Results

Question 2

Name an advantage of a Within-subjects Anova:

Answer 2

Controls for Individual Differences
between participants

Question 3

Name some disadvantages of a Within-subjects Anova:

Answer 3

Risk of carry over effects

Question 4

We can conduct extra tests to find out where these differences are:

Answer 4

Planned (a priori) comparisons
this is a more robust way of testing
consistancy

Unplanned (post hoc) comparisons

Question 5

What if I had significant main effects or interactions?

Answer 5

Depends on if your data had planned or unplanned comparisons…

Planned comprisons
Can be conducted on main effects and interactions

Unplanned comparisons
Post-hoc tests can be conducted on main effects
For interactions you would need to conduct simple main effects analysis.