MANOVA vs ANOVA Flashcards
What are the disadvantages of manova?
:( More complex than anova
:( manova has more a more complex set of assumptions than anova that are less easily satisfied, these need to be tested for
:( ambiguous outcomes
:( Cole at al. (1994)- complex factors affect power, manova generally has lower power (apart from in rare cases)
what are the advantages of manova?
:) multiple DVs increases the chance of finding an effect, and manova can tell you which DVs are important
:) Manova is just one analysis, whereas the multiple analyses in anovas inflates the Type 1 error rate (familywise error, 1-(1-a)to the power of c)- would need to adjust for multiple comparisons e.g for 3 DVs, alpha= .05/3
(BUT lower power in manova can override this)
When does manova have more power?
:) In RARE cases, manova can be more powerful than anova and show you effects that are not revealed by anova
(there might be a lot of overlap between 2 groups on DV1 and DV2, but manova separates out the groups as much as possible on the LC- ellipses show not much overlap)
What determines manova power?
(Cole et al., 1994)
Power is determined by a combination of the correlation between the DVs, and the direction of the effect of the DVs that the group factor has
Is it expected that the DVs will be correlated witch each other?
manova with more power: example 1
If 2 DVS are POSITIVELY correlated, it is for the effect of IV to be in DIFFERENT direction.
DV1: group1 > group2
DV2: goup1 < group2
:( will be LESS POWERFUL (more overlap of ellipses, harder to discriminate) if they are in the SAME direction
manova with more power: example 2
If 2 DVs are NEGATIVELY correlated, manova is MORE POWERFUL if the IV-DV relationships is in the SAME direction for both DVs
(e.g. group A score higher on both DVs, which are negative correlated)
Ellipses will overlap less, easier to discriminate between groups
DV1: group1 > group2
DV2: group1 > group2
