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Re: st: linear and quadratic trend analysis


From   David Jacobs <jacobs.184@sociology.osu.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: linear and quadratic trend analysis
Date   Wed, 05 Mar 2008 12:18:28 -0500

I'm not sure that Martin answered your question although you probably already know what I'm about to say.

To control for a linear trend simply construct a counter explanatory variable running from 1 to how many years you have; to test a quadratic, add the square of this explanatory variable and so on for a cubic.

As analysis of variance allows continuous explanatory variables, this can be done in anova although most people probably would use regress. If you use a quadratic or cubic it would be a good idea to test the relevant terms for joint significance. That will help you decide if the higher order term is necessary.

Dave Jacobs

At 03:49 PM 3/4/2008, you wrote:

Hi there,
I am conducting a study using the National AddHealth data set. After running factorial anovas, it is clear that I need to follow up with a trend analysis. I figured out how to run graphs, but does anyone have information on running the statistical tests for trends. The study has four continuous outcome variables, plus sex, age, and grade level with one categorical independent variable. Any help is much appreciated.
Shelly

Shelly Mahon
Ph.D. Candidate
University of Wisconsin-Madison
Human Development and Family Studies
1430 Linden Drive
Madison, WI 53706-1575
email: mdmahon@wisc.edu

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