Effects - plot the marginal effect
Dear Tomas, Write the model as mreg01 = lm(enep1 ~ enpres * proximity1), data=a90) 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 <diogenas at 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