Re: [S] I, me, my

John Thaden (
Mon, 02 Mar 1998 10:11:17 -0600

I() is the identity function and results in its argument (abund^2) being
treated "as is". This may seem silly, but consider when the argument is a
product: So a regression formula written as response ~ I(abund*height) has
a single predictor, the product of abund and height, but response ~
abund*height has three predictors and might also be written as response ~
abund + height + abund:height. Your formula was probably something like
predictor ~ abund^2. The function lm() was smart enough to interpret this
"as is", and it listed the grammatically safer version in its output.

John Thaden, Biochemist
Department of Geriatrics
University of Arkansas for Medical Sciences
Little Rock AR

At 11:32 PM 3/1/1998 -0700, you wrote:
>Can anyone tell me what it means when the output (summary) of a lm gives
>a coefficient for a polynomial term in parentheses with an "I" in front
>of it, for example: I(abund^2) ?
>Steve Bousquin
>Colorado State University
>Department of Rangeland Ecosystem Science/GDPE
>Fort Collins, CO 80523
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