[R] New variables "remember" how they were created?

[Adaikalavan Ramasamy]

Your example is too complicated for me. But few points:

1) What do you mean by "instrument"? Do you mean variable?

2) diff(demand) is identical to demand[-1] - demand[-204]

3) system() is a built-in R function, so avoid using it as variable name

4) The variable "yd" is in the eqInvest formula and subsequently to the 
system formula. The variable "y.1" is in the instruments formula. Both 
formulas are passed onto systemfit() call. Thus I see no surprises here.

Try simplifying and rephrasing please if you want further help.

Regards, Adai




Skipper Seabold wrote:
> Hello all,
> 
> I hope this question is appropriate for this ML.
> 
> Basically, I am wondering if when you create a new variable, if the
> variable holds some information about how it was created.
> 
> Let me explain, I have the following code to replicate an example in a
> textbook (Greene's Econometric Analysis), using the systemfit package.
> 
> dta <- read.table('http://pages.stern.nyu.edu/~wgreene/Text/Edition6/TableF5-1.txt',
> header = TRUE)
> attach(dta)
> library(systemfit)
> demand <- realcons + realinvs + realgovt
> c.1 <- realcons[-204]
> y.1 <- demand[-204]
> yd <- demand[-1] - y.1
> eqConsump <- realcons[-1] ~ demand[-1] + c.1
> eqInvest <- realinvs[-1] ~ tbilrate[-1] + yd
> system <- list( Consumption = eqConsump, Investment = eqInvest)
> instruments <- ~ realgovt[-1] + tbilrate[-1] + c.1 + y.1
> # 2SLS
> greene2sls <- systemfit( system, "2SLS", inst = instruments,
> methodResidCov = "noDfCor" )
> 
> When I do the 2SLS fit, it seems that even though I declared y.1 as an
> instrument that the estimator "knows" that yd was created using y1, so
> it (correctly) transforms yd to use the instrument in the final
> estimation.
> 
> So I'm wondering if yd somehow carries knowledge of how it was created.
> 
> Thanks,
> 
> Skipper
> 
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