Analysis of Covariance. 46-512: Statistics for Graduate Study in Psychology. Learning Outcomes. What is an ANCOVA? How does it relate to what we have done already? When would we use it? What are the issues & assumptions? What are some limitations and alternatives?.
Analysis of Covariance
46-512: Statistics for Graduate Study in Psychology
Treat group 3 as control:
DC1 identifies Group 1
DC2 identifies Group 2
if (gpid=1) dc1=1.
if (gpid=2) dc2=1.
/DESCRIPTIVES MEAN STDDEV CORR SIG N
/STATISTICS COEFF OUTS CI R ANOVA
/METHOD=ENTER dc1 dc2 .
R2 = 204.056/1600.306 = .128
Enter our continuous variable (IQ)
Sans interaction term for the time being.
R2 = .527
Why is GPID now significant?
Adjusted Means calculated as…
For Group 1…
Compare to those from our MRA
BPcrit = 3.55, Cell 3 is significantly higher than 1 & 2
Bryant-Paulson is an extension of Tukey’s Post-Hoc test, and more appropriate if X is random.
For now, we will suspend discussion of more complicated designs, but revisit when we cover MANOVA and MANCOVA