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==Correlation of dependent variables==
[[File:Outcome Variables.jpg|thumb|This is a graphical depiction of the required relationship amongst outcome variables in a multivariate analysis of variance. Part of the analysis involves creating a composite variable, which the group differences of the independent variable are analyzed against. The composite variables, as there can be multiple, are different combinations of the outcome variables. The analysis then determines which combination shows the greatest group differences for the independent variable. A descriptive discriminant analysis is then used as a post hoc test to determine what the makeup of that composite variable is that creates the greatest group differences.]]
[[File:MANOVAs and Highly Correlated Dependent Variables.png|thumb|This is a simple visual representation of the effect of two highly correlated dependent variables within a MANOVA. If two (or more) dependent variables are highly correlated, the chances of a Type I error occurring is reduced, but the trade-off is that the power of the MANOVA test is also reduced.]]
MANOVA's power is affected by the correlations of the dependent variables and by the effect sizes associated with those variables. For example, when there are two groups and two dependent variables, MANOVA's power is lowest when the correlation equals the ratio of the smaller to the larger standardized effect size.<ref>{{cite journal|last1=Frane|first1=Andrew|title=Power and Type I Error Control for Univariate Comparisons in Multivariate Two-Group Designs|journal=Multivariate Behavioral Research|volume=50|issue=2|pages=233–247|date=2015|doi=10.1080/00273171.2014.968836|pmid=26609880}}</ref>
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