Posted by
Rich Ulrich on
Apr 20, 2011; 6:27pm
URL: http://spssx-discussion.165.s1.nabble.com/Discriminant-function-analysis-tp4315226p4328892.html
>
> I've done a discriminant function analysis in SPSS intended to classify 3
> types of case using 30 variables. The discriminant function coefficients and
> structure matrix are below. It is clear that the two functions do different
> things with these data. I have the following questions:
The important message from *your* standardized coefficients is
that several of them are greater than 1.0; and they occur in pairs
of related variables. Like in regression (though the standardization
is slightly different), these demonstrate that you have suppressor
variables.
> S3DUR -1.906 .829
> S4DUR 1.546 -.843
> RPVI1TO4 -.200 1.226
> NPVI1TO4 .082 -1.588
SxDUR and xPV1TO4 comprise pairs that have similar structure
coefficients (which are correlations), but different directions (+,-)
when used in the equation. If you want an easy interpretation,
I suggest that you redo the analysis where these variables are
replaced, each pair, by a difference and a sum (or average).
Suppressors can be created by more than two variables, and they
don't have to have the same scaling for each variable; those
conditions can make dealing with them more confusing, at the least.
Your data seems to have the simpler version, if I judge correctly
from the variable names.
> 1. How do I identify what each function is doing when cases are classified?
> 2. I want to calculate on a case by case basis the scores for truncated
> forms of each discriminant function (f1 S1DUR - S3PIRANG and f2 S3INRANG
> -RPVIS1). I assume I generate a linear equation using these coefficients to
> weight each variable. Is that right?
> 3. Alternatively, is there a simple way of obtaining the scores from each
> case for each discriminant function by procedures in SPSS? On reflection,
> this might be the preferred option, but I will stand to be advised.
>
SPSS can give you certain predicted scores, and it can list them by case.
You will have to read up on the subject, to figure out what you are
getting from "classification equations", if you use those.
I can't tell what else you are asking here. You can also write explicit
equations in SPSS syntax, if you obtain the not-standardized coefficients.
--
Rich Ulrich
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