Repeated measures ANOVA Flashcards
When would we use a repeated measures ANOVA?
Looking at differences between three or more levels of one within-groups factor
Data at interval level and parametric assumptions met
Why is the repeated measures design advantageous?
More powerful because each participant is its own control, reducing error and variation within groups
What do we want to keep to a minimum?
Unexplained error, attributable to ways that different participants vary across conditions other than because of the IV
This ERROR VARIATION can be broken up into error and “variation among participants” because we are using repeated measures - we are reducing the unexplained variance on the bottom of the F statistic and thus producing a larger value
How can we reduce error?
By explaining SOME of the variation that is not due to the IV - we need to PARTITION THE SUM OF THE SQUARES
How do we partial our variance?
TOTAL VARIATION (SS) - SS of deviations of all scores around grand mean BETWEEN SUBJECTS SS - variation of participants average scores BETWEEN CONDITIONS SS - variation of means of different conditions ERROR SS - represents how subjects interact with conditions i.e. extent to which all subjects DON'T go the same way as each other across conditions
The final two here come under the umbrella of within subjects SS
What is the assumption of schericity?
That the variances of the differences between all possible pairs of levels of the IV are equal
Because the same participants are performing in each level you would assume that the correlations between all possible combinations of levels are roughly the same
This test is valuable where there are 3 or more levels
Use Mauchley’s test and if significant it means assumption violated (look at multivariate statistics in this case)
What does N represent in repeated measures?
All scores, NOT number of participants
So we may have five participants, and 3 conditions, so the total scores (N) is 15
Describe the process of repeated measures ANOVA
Find SStotal Find SSsubjects Find SS conditions Find SSerror Find degrees of freedom for total, subjects, conditions and error
F=MSconditions/MS error
(see formula sheet for how to work all of these things out)
