[R] Q - scatterplot, plot function & trellis linear regressions???

[Jhope]

Thank you Simon, 
Yes this was in the library(car). There were no negative values in the
scatterplot graph or negative limits displayed.

Q-2 Are you sure the lines from the scatterplot are not this?:
solid green line: linear regression
solid red line: non-linear regression
upper dashed red line: upper limits 75 percentile
lower dashed red line: lower limits 25 percentile

Q-3 
I am trying to make a trellis of linear regressions but unsuccessful . I
want 3 windows displaying 3 events of linear regression (two-way
interactions). I have been trying this: 

require(lattice) 
> library(lattice) 
> trellis.par.set(col.whitebg()) 
> scatterplot(DevelopIndex~Veg|Aeventexhumed, 
+             xlab = "Distance to vegetation border", 
+             ylab = "Embryonic development index") 
Error in eval(expr, envir, enclos) : object 'DevelopIndex' not found 

This error appears and I am not able to produce the trellis of 3 windows
displaying 3 events of linear regressions. 

Please advise
Thank you, Jean

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