topic Re: Type III test and LSMeans in Proc GLM for ANCOVA model do not agree in New SAS User

Type III test and LSMeans in Proc GLM for ANCOVA model do not agree

fdehkord — Fri, 15 Jul 2022 17:18:10 GMT

Hello,

I am new to Proc GLM and would appreciate help answering the following question.

I have fitted an ANCOVA model with covariate X (continuous) and two factors A and B (each with two Levels). The relationship between Y (the continuous response variable) and X is not linear therefore I have included a quadratic term for X in the model and included the interaction term x*A*B in the model as well.

The type III F-test is significant for Factor A but not significant for factor B. The interaction term X*A*B is statistically significant and x and x2 are also significant.

The LSMEANS test for Factor A is not significant while it is significant for factor B ( the opposite of Type III F-test).

Why is this?

Re: Type III test and LSMeans in Proc GLM for ANCOVA model do not agree

PaigeMiller — Sat, 16 Jul 2022 10:49:22 GMT

Show us the output from your PROC GLM. Use the "Insert Photos" icon to include a screen capture of your output in your reply — do not attach files.

Re: Type III test and LSMeans in Proc GLM for ANCOVA model do not agree

Rick_SAS — Sun, 17 Jul 2022 10:28:08 GMT

Interpreting higher-order interactions can be a challenge if you have not included the lower-order interactions. Have you also included the second-order interactions x*A, x*B, and A*B? Show use your GLM code.

Re: Type III test and LSMeans in Proc GLM for ANCOVA model do not agree

fdehkord — Mon, 18 Jul 2022 17:19:10 GMT

Re: Type III test and LSMeans in Proc GLM for ANCOVA model do not agree

fdehkord — Mon, 18 Jul 2022 17:20:56 GMT

Here it is

Thanks.

Re: Type III test and LSMeans in Proc GLM for ANCOVA model do not agree

fdehkord — Tue, 19 Jul 2022 00:34:14 GMT

I did include the lower-order terms and still have the same problem.