On Apr 8, 2011, at 4:24 AM, Tomii wrote:
Thank you for your response, but these changes doesn't seem to change
anything, outcomes of effect command is still the same - error.
Tomas
On Fri, Apr 1, 2011 at 5:03 AM, John Fox <j...@mcmaster.ca> wrote:
Dear Tomas,
Write the model as
mreg01 = lm(enep1 ~ enpres * proximity1), data=a90)
A syntactic comment only. Perhaps:
mreg01 = lm(enep1 ~ enpres * proximity1, data=a90)
--
David
That is, it's not necessary to index a90 as a list since it's given
as the
data argument to lm, and doing so confuses the effect() function.
Also,
enpres*proximity1 will include both the enpres:proximity1
interaction and
enpres + proximity1, which are marginal to the interaction.
Next, you must quote the name of the term for which you want to
compute
effects, thus "enpres:proximity1" in the call to effect().
Finally, effect() doesn't compute what are usually termed marginal
effects.
If you want more information about what it does, see the references
given in
?effect.
I hope this helps,
John
------------------------------------------------
John Fox
Sen. William McMaster Prof. of Social Statistics
Department of Sociology
McMaster University
Hamilton, Ontario, Canada
http://socserv.mcmaster.ca/jfox/
On Thu, 31 Mar 2011 22:09:32 +0200
Tomii <dioge...@gmail.com> wrote:
Hello,
I try to plot the marginal effect by using package
"effects" (example of
the
graph i want to get is in the attached picture).
All variables are continuous.
Here is regression function, results and error effect function
gives:
mreg01 = lm(a90$enep1 ~ a90$enpres + a90$proximity1 + (a90$enpres *
a90$proximity1), data=a90)> summary(mreg01)
Call:
lm(formula = a90$enep1 ~ a90$enpres + a90$proximity1 + (a90$enpres *
a90$proximity1), data = a90)
Residuals:
Min 1Q Median 3Q Max
-2.3173 -1.3349 -0.5713 0.8938 8.1084
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 4.2273 0.3090 13.683 < 2e-16 ***
a90$enpres 0.4225 0.2319 1.822 0.072250 .
a90$proximity1 -3.8797 1.0984 -3.532 0.000696 ***
a90$enpres:a90$proximity1 0.8953 0.4101 2.183 0.032025 *
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 2.029 on 78 degrees of freedom
Multiple R-squared: 0.2128, Adjusted R-squared: 0.1826
F-statistic: 7.031 on 3 and 78 DF, p-value: 0.0003029
plot(effect(a90$enpres:a90$proximity1, mreg01))Warning messages:
1: In
a90$enpres:a90$proximity1 :
numerical expression has 82 elements: only the first used2: In
a90$enpres:a90$proximity1 :
numerical expression has 82 elements: only the first used3: In
analyze.model(term, mod, xlevels, default.levels) :
0 does not appear in the modelError in
plot(effect(a90$enpres:a90$proximity1, mreg01)) :
error in evaluating the argument 'x' in selecting a method for
function
'plot'
Thanks in advance.
Tomas
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