[R] when to use "I", "as is" caret

[agent dunham]

Dear community, 

I've check it while working, but just to reassure myself.  Let's say we have
2 models: 

model1 <-  lm(vdep ~ log(v1) + v2 + v3 + I(v4^2) , data = mydata)
model2 <-   lm(vdep ~ log(v1) + v2 + v3 + v4^2, data = mydata)

So in model1 you really square v4; and in model2,  v4*^2 *doesn't do
anything, does it? Model2 could be rewritten:
model2b <-   lm(vdep ~ log(v1) + v2 + v3 + v4, data = mydata) and nothing
changes, doesn't it?

This "I" caret is essential with powering or when including transformations
as I(1/(v2+v3)) but not with log transformation, isn't it?. Is there any
other transformation where I muss use also this "I", as is caret?

Thanks in advance, 
user at host.com



--
View this message in context: http://r.789695.n4.nabble.com/when-to-use-I-as-is-caret-tp4643113.html
Sent from the R help mailing list archive at Nabble.com.