[R] Fitting linear models

[David Winsemius]

On Apr 21, 2009, at 12:37 PM, Vemuri, Aparna wrote:

> These are all field measured values.
> For a little background here, I have field measurements of SO4, NO3  
> and NH4. I used these variables in an atmospheric chemistry model to  
> calculate PBW on a line-by-line basis.
>
> To bypass the use of the complex atmospheric chemistry model in the  
> future, I want to develop a regression equation based on the current  
> results I have.  Also, I know the atmospheric chemistry model  
> requires SO4, NO3 and NH4 to estimate PBW. So I am using the same as  
> IVs for the regression model.
> Aparna

One way to create collinearity is to construct a new variable, say  
PBW?,   as a linear combination of the measurements. If you then re- 
analyze that augmented dataset, you will naturally get the sort of  
complaints or unexpected behavior from the R interpreter that you are  
seeing.

-- 
David Winsemius