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Re: st: Graph Quadratic Term
From
Steven Samuels <[email protected]>
To
[email protected]
Subject
Re: st: Graph Quadratic Term
Date
Tue, 19 Apr 2011 12:48:21 -0400
Dennis,
Quadratic trends can look linear. If you print out the graph and lay a ruler over the extreme points, what do you see?
Steve
[email protected]
On Apr 18, 2011, at 1:00 PM, Nick Cox wrote:
I don't know what you mean by "does not plot correctly" and in any
case you give very little code.
-predict- is a command, not a function.
This example may help
sysuse auto
gen headroomsq = headroom^2
logit foreign headroom headroomsq
predict predict, pr
scatter foreign headroom || mspline predict headroom
A quadratic on the logit scale naturally translates to a bell-shape on
the original scale.
Nick
On Mon, Apr 18, 2011 at 5:36 PM, Dennis Kramer <[email protected]> wrote:
> I am having trouble graphing the quadratic relationship between my
> outcome dependent and independent variable. I am currently modeling a
> -logit- function with my outcome being 0/1 for passing a standardized
> test. When I run my --logit-- with the sq term in the model I get a
> significant quadratic function; however, when I use the -- predict, pr
> -- function to plot for predictions the quadratic function does not
> plot correctly... could you provide some insight.
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