Re: interpretation categorical variables

["Friedman, Emil" <efriedman@mannkindcorp.com>]

You are apparently using stepwise.  The dummy variable Soil{4&3&1 - 6&7&5} compares the average of soils 4,3, and 1 to the average of soils 6,7 and 5.  If you use standard least squares JMP will create a different set of dummy variables and it will also let you compare the different soils in a more intuitive manner.  Stepwise is mostly used if you are trying to find a model containing fewer terms than the full model. 

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Emil M Friedman, PhD
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http://www.statisticalconsulting.org

 

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From: jmp-l-owner@lists.biostat.wustl.edu [mailto:jmp-l-owner@lists.biostat.wustl.edu] On Behalf Of Tom Vanwalleghem
Sent: Wednesday, July 16, 2008 3:37 PM
To: jmp-l@wubios.wustl.edu
Subject: [jmp-l] interpretation categorical variables

Dear list-users,

 

I´m afraid this could be a basic question, but I did not find the answer to my question in the jmp help files, so I turn my hopes to this list.

I have fitted a multiple regression model with continuous and categorical variables and have some problems with the interpretation of the output.

 

My variable is soil class (soil - 7 classes).

How do I interpret this dummy variable JMP creates: " Soil{4&3&1 - 6&7&5} "

 

I found some examples with two cases, eg. " manager{a-b}", which make sense, but I have some troubles with the interpretation of this more complex variable.

Any help is therefore strongly appreciated.

 

Tom Van Walleghem

 

Departamento de Agronomía
Escuela Técnica Superior de Ingenieros Agrónomos y Montes

Universidad de Córdoba 
Avda. Menendez Pidal s/n
14080 Córdoba 
España