Solved – Correlation between dependent variable and the covariate in an ANCOVA

ancova

I want to check the effect that a categorical between-subjects factor A and a continuous predictor B has on a certain dep. variable. I created an ANCOVA with A as a factor and B as a covariate. This should tell me whether there is a main effect of A on the DV, but is this ANCOVA the correct statistical model to use in order to see if B also has an effect on the DV, in other words if A correlated with the DV?

Best Answer

Yes. It is just a regression equation, after all. You can look at the table of coefficients (or "solution", in some software) to see the estimate and $t$ test of the coefficient of $B$. This will test the contribution of $B$, after adjusting for $A$.

Related Solutions

Solved – Difference between ANCOVA and Hierarchical Regression

There really isn't a difference. In matrix algebra form, regression, ANOVA and ANCOVA are all written as

$Y = X\beta + \epsilon$

They arose in different fields and the output is typically formatted differently, but the meaning is the same. However, in the usual usage of the words, regression incorporates the other two, because ANOVA is usually used only when all the independent variables are categorical; ANCOVA when one is continuous (usually) and the others categorical, and regression for any IVs at all.

Solved – ANCOVA to check effect of covariate

Why not just:

#Is group important?
m1 <- with(data, lm(response~as.factor(group)))
summary(m1)
#Is age important and does it affect the effect of group?
m2 <- with(data, lm(response~as.factor(group)+age))
summary(m2)
#Does age affect the effect of group?
anova(m1,m2)

These are three different questions. In this case, all three are important, but to different degrees.

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Related Solutions

Solved – Difference between ANCOVA and Hierarchical Regression

Solved – ANCOVA to check effect of covariate

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