week 3 ANCOVA

Question 1

how do you determine if C is a usefull covariate?

Answer 1

• check if there is a relation between X and C (ANOVA, test between subjects)
• Correlation between C and Y?–>yes?–>Adding C will reduce error variance (good thing)

Question 2

what is the function of this graph?

ANCOVA

Answer 2

• check the slopes for suspision of parallelism
• In this graph we see suspision of an interaction, because the lines are not completely parallel.

Question 3

using this ANCOVA table. can the null hypothesis of parallel regression lines be rejected?

Answer 3

NO–>interaction is non sign–>regression lines between C and Y have the same regression weight.