Estimating slopes and intercepts in ANCOVA

abh1

I am feeling particularly dumb today and hope someone can help me feel smarter.  When running an ANCOVA with separate slopes, I would like to get estimates of the slopes and intercepts of each group along with the t-tests of significance.  In SAS, I can run GLM and specify the model like this (using the JMP "Drug" data table):

model y = Drug Drug*x / noint solution;

 

I cannot find anything in JMP that is comparable to this.  Specifying the same model above in the Fit Model dialog gives me something totally unlike what SAS gives.  I have tried displaying indicator parameter estimates, extended estimates, and pretty much everything this is under the "Effects" menu item in the Fit Model results window.  I realize that JMP parameterizes the model differently than SAS, but I have not yet found the correct combination of model specification and options to duplicate the SAS results.  I also realize that one can figure out what the slopes and intercepts are from the parameter estimates table, but the tests are testing whether the deviations are significantly different from zero, not whether the group slopes and intercepts are different from zero (unless I am actually dumber than I feel today).

 

Mark_Bailey

I just used the JMP example Big Class. I used Analyze > Fit Model to specify the model and then clicked the red triangle to select Submit to SAS. This program is what JMP created for me.

 

DATA Big_Class; INPUT  sex &$ height weight; Lines;
F  59  95  
F  61  123  
F  55  74  
F  66  145  
F  52  64  
M  60  84  
M  61  128  
M  51  79  
F  60  112  
F  61  107  
F  56  67  
M  65  98  
M  63  105  
M  58  95  
M  59  79  
F  61  81  
F  62  91  
F  65  142  
F  63  84  
F  62  85  
M  63  93  
M  64  99  
M  65  119  
M  64  92  
M  68  112  
M  64  99  
M  69  113  
F  62  92  
F  64  112  
M  67  128  
M  65  111  
M  66  105  
M  62  104  
M  66  106  
F  65  112  
F  60  115  
M  68  128  
F  62  116  
M  68  134  
M  70  172  
;
RUN;

PROC GLM  DATA=Big_Class ALPHA=0.05;
CLASS sex;
MODEL  weight =  sex height sex*height / noint solution;
RUN;

 

Here is the SAS output:

 

 

First of all, you requested a linear model without an intercept. Simply check this option in the middle of the bottom of the Fit Model launch dialog. Click the red triangle and deselect Center Polynomials. Click Run. Then click the red triangle at the top and select Estimates > Expanded Estimates.

 

Here is the JMP output:

 

 

The estimates are different because JMP parameterizes the terms differnently than PROC GLM. Is this report what you are looking for?