Chp13 ANCOVA Flashcards
What is ANCOVA?
When linear model used to compare multiple means adjusted for the effect of covariates
What are covariates?
An observed continuous score that adds variation to the outcome.
What are confounds?
variables other than the experimental manipulation that effect outcomes
how is within group variance decreased in ANCOVA?
Some of the unexplained variance is attributed to covariates.
What will a lack of independence do to ANCOVA?
It may bias the ANCOVA
five step General procedure for ANCOVA
Explore data, check independance and homogeneity of regression slopes, ANCOVA, follow up tests, effect size
Explore data for ANCOVA
check for outliers, homogeneitey, normality with boxplots, histograms and descriptive statistics
If covariate and treatment variable are not independent…
correct problems and do ANCOVA OR use robust ANCOVA
If heterogeniety of regression slopes
use a multi-level model
What follow up tests are done after ANCOVA
specific hypothesis do planned comparisons
no specific hypothesis do post hoc tests
ANCOVA: effect size
Partial eta squared
What does partial eta squared do?
examines the proportion of variance that a variable explains compared to what isn’t explained by other variables.
