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Re: PSPP linear regression (reference category).

From: Alan Mead
Subject: Re: PSPP linear regression (reference category).
Date: Thu, 29 Sep 2016 09:39:47 -0500
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0

If I understand your question, you're asking which is is the category against which each other dummy-coded category is compared? 

You select it when you dummy code.  When you have K categories, you create K-1 dummy variables and one group has a zero on all K-1 dummy variables.  That group is the reference group.

Think about it... the model for that group is missing the dummy coded variable and each of the remaining K-1 variables each have a regression coefficient that compares them to the reference group.


On 9/29/2016 9:13 AM, Jack Drew wrote:
I use PSPP (current version 0.10.2) to generate linear regression models.  But, after checking the manual and help archive, I'm still having difficulty understanding how PSPP treats the reference categories for dummy variables, and if/how/what PSPP options let you set the reference.

Please could someone be kind enough to explain this feature in PSPP.

Thank you.  Jack

Jack Drew
Senior Institutional Research Analyst
Office of Institutional Research
Mott Community College

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Alan D. Mead, Ph.D.
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