Re: GLM repeated measures concern/question

Posted by eyeman03 on Jan 09, 2012; 2:14pm
URL: http://spssx-discussion.165.s1.nabble.com/GLM-repeated-measures-concern-question-tp5104022p5131418.html

First, thank you EVERYONE for your input.  It’s really appreciated.    

Diana,

Let me expand a little on the design.  We are studying the effects of two types of simulated central blind spots on adaptation.  The task is Visual Search with 3 set sizes (1, 8, 32)  

The research design is a mixed 2x2 ANOVA with adaptation as the within effect, and blind spot type as the between effect.  The statistical tool is GLM Repeated measures.          

As you know, our problem is the unequal spacing of the set sizes, and whether or not SPSS intrinsically recognizes the spacing as equal.   You answered that question; yes, it does.

We’ve come to learn we can use the CONTRAST option for set size.  However, If we add set size as a covariate (as you suggested), then SPSS will not recognize it as a factor (CONTRAST).

But if set size is added as a Between-Subject factor , we can now write syntax as a CONTRAST:  /CONTRAST(Set size)=Polynomial (1, 8, 32).

We ran two different syntaxes to compare their CONTRAST results. : /CONTRAST(Set size)=Polynomial (1, 8, 32) vs /CONTRAST(Set size)=Polynomial.  

With the former syntax, only the linear contrast was significant.   With the latter syntax, both the linear and quadratic contrast were highly significant.  

So the output analysis with stating vs not stating the set sizes made a significant difference.  
We wanted to ask you opinion if this syntax solution: CONTRAST POLYOMIALS (1, 8, 32) seems correct for our analysis

Dave

PS……I can send the Output data if anyone is interested.