On Wed, 9 Nov 2005, CG Pettersson wrote:
Hello all,
R2.1.1, Wk2
^^^ week 2?
I am doing some two-step plotting, first using plot() to illustrate the
datapoints and then using abline() to place a trend line from a fitted
model into the plot.
Everything works well as long as the formula of the fitted model i of the
type:
m1 - lm(Dependent ~ Independent)
then abline(m1) puts the proper straight line into the plot.
But if I use:
m2 - lm(Dependent ~ Independent + I(Independent^2))
abline(m2) produces a straight line, only from the first order term.
Why, and what should I do about it?
Why: because that is what it is documented to do:
'reg' is a regression object which contains 'reg$coef'. If it is
of length 1 then the value is taken to be the slope of a line
through the origin, otherwise, the first 2 values are taken to be
the intercept and slope.
What to do about it: first, read the help page and second, use predict and
lines. There is an example of the latter on ?cars.
--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UKFax: +44 1865 272595
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