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11-28-2015 10:59 AM

Hi all, i've a problem:

i'm using a node of regression in SAS EM WORKSTATION 12.1; I'm using a cross-validation method and my aim is getting a logistic regression with the possible insertion of significant interactions.

So my settings are:

principal effect--> YES

2 factors interactions -->yes

polynomial terms -->yes

maximum degree of polynomial terms = 2

regression kind = logistic regression

selection method= stepwise

selection criterion= crossvalidation error (this bcs i'm using cross-validation)

The final model proposed is:

Intercept Gravidanze*Pedigree IMP_BMI*IMP_Diastolica IMP_BMI*IMP_Glucosio IMP_Insulina*Pedigree

(for the full output see the attachment stattalk.txt)

So all my effects are interactions of quantitative variable ad no principal effect seems to be significant.

I'm trying to find an explanation to this output.. can someone help me?

But that's not all, because if i modify settings and sat up "2 factor interactions-->NO" (I do not modify others settings)

and i run the node i obtain the same output.. ..so i think there is something wrong, but can someone tell me what?

i wait for some advice Smiley Happy

thank you in advance!

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Solution

12-01-2015
01:26 PM

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12-01-2015 12:52 PM

**Use Selection Defaults** to *No*, then click on the ellipsis for **Selection Options**. There you can change **Hierarchy Effects** to *All *then select *Single* for the **Moving Effect Rule** property. Hope that does the trick!

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12-01-2015 09:39 AM

I'm guessing those terms you are seeing that include 2 inputs are actually polynomial terms (those are "interactions" of the interval inputs), so you need to set Polynomial Terms to No as well if you don't want any interaction effects. The Two-Factor Interactions property applies to interactions involving the class inputs only.

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12-01-2015 12:40 PM

Ok thanks a lot, now i understand why using the setting "two Factor Interaction" or not my output was the same!

Althought my problem is that that a model with only interactions (in my opininion) has no sense: interaction has sense only if also principal effects are significant in the model. So now my new question is:

how could i tell EM to use a hierarchic procedure while it puts variables into the model?

I mean how can i tell it FIRST to enter significant principal effects and only THEN interactions (between princ. eff. wihch had entered as significant)?

I imagine that i should modify the settings in "use default selection values" in model selection panel but, what should i modify in particular?

Again, thank you in advance!

Solution

12-01-2015
01:26 PM

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12-01-2015 12:52 PM

**Use Selection Defaults** to *No*, then click on the ellipsis for **Selection Options**. There you can change **Hierarchy Effects** to *All *then select *Single* for the **Moving Effect Rule** property. Hope that does the trick!

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12-01-2015 01:26 PM

Perfect! thank you again!