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) > > 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 â***â 0.001 â**â 0.01 â*â 0.05 â.â 0.1 > > â â 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 > > > > [[alternative HTML version deleted]]
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