Your script ran for me without error under the following configuration:

> sessionInfo()
R version 2.9.1 (2009-06-26)
i386-pc-mingw32

locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United States.1252;LC_MONETARY=English_United States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252

attached base packages:
[1] splines stats graphics grDevices utils datasets methods
[8] base

other attached packages:
[1] plm_1.1-4 sandwich_2.2-1 zoo_1.5-6 MASS_7.2-47
[5] Formula_0.1-3 kinship_1.1.0-22 lattice_0.17-25 nlme_3.1-92
[9] survival_2.35-4

loaded via a namespace (and not attached):
[1] grid_2.9.1 tools_2.9.1


I suggest you upgrade to R 2.9.1.


By the way, I did not know about "plm". To find that function, I proceeded as follows:


library(RSiteSearch)
plm. <- RSiteSearch.function('plm')
HTML(plm.)


This identified 82 different help pages in 11 different packages; 38 matches were found in the "plm" package, which contained a function called "plm". I assume this is the one you were using.


Hope this helps.
Spencer Graves


Damien Moore wrote:
Hi List

I'm having difficulty understanding how plm should work with dynamic
formulas. See the commands and output below on a standard data set. Notice
that the first summary(plm(...)) call returns the same result as the second
(it shouldn't if it actually uses the lagged variable requested). The third
call results in error (trying to use diff'ed variable in regression)

Other info: I'm running R 2.7.2 on WinXP

cheers



*>data("Gasoline",package="Ecdat")
Gasoline_plm<-plm.data(Gasoline,c("country","year"))
pdim(Gasoline_plm)
**Balanced Panel: n=18, T=19, N=342
*
*>summary(plm(lgaspcar~lincomep,data=Gasoline_plm**))
**Oneway (individual) effect Within Model

Call:
plm(formula = lgaspcar ~ lincomep, data = Gasoline_plm)

Balanced Panel: n=18, T=19, N=342

Residuals :
    Min.  1st Qu.   Median  3rd Qu.     Max.
-0.40100 -0.08410 -0.00858  0.08770  0.73400

Coefficients :
         Estimate Std. Error t-value  Pr(>|t|)
lincomep -0.76183    0.03535 -21.551 < 2.2e-16 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Total Sum of Squares: 17.061
Residual Sum of Squares: 6.9981
Multiple R-Squared: 0.58981
F-statistic: 464.442 on 323 and 1 DF, p-value: 0.036981

**> summary(plm(lgaspcar~lag(lincomep),data=Gasoline_plm))
**Oneway (individual) effect Within Model

Call:
plm(formula = lgaspcar ~ lag(lincomep), data = Gasoline_plm)

Balanced Panel: n=18, T=19, N=342

Residuals :
    Min.  1st Qu.   Median  3rd Qu.     Max.
-0.40100 -0.08410 -0.00858  0.08770  0.73400

Coefficients :
              Estimate Std. Error t-value  Pr(>|t|)
lag(lincomep) -0.76183    0.03535 -21.551 < 2.2e-16 ***
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Total Sum of Squares: 17.061
Residual Sum of Squares: 6.9981
Multiple R-Squared: 0.58981
F-statistic: 464.442 on 323 and 1 DF, p-value: 0.036981

*
*>summary(plm(lgaspcar~diff(lincomep),data=Gasoline_plm))*
*Error in model.frame.default(formula = lgaspcar ~ diff(lincomep), data =
mydata,  :
  variable lengths differ (found for 'diff(lincomep)')
*

        [[alternative HTML version deleted]]

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