plotting log regression

Your example seems strange because a line fits on the x-y scale; not on the log(x)-log(y) scale.  Anyway, here is my example.  You can build on it for more general data.

x <- exp(1:10)
y <- exp(10:1 + rnorm(10))


logmod <- lm(log(y)~log(x))
logypred <- predict(logmod)


plot(y~x)
lines(exp(logypred)~x, col=2)


plot(y~x, log="xy")
lines(exp(logypred)~x, col=2)

Chris


-----Original Message-----
From: Rui Barradas [mailto:ruipbarradas at sapo.pt] 
Sent: Friday, December 14, 2012 12:06 PM
To: mrkooper
Cc: r-help at r-project.org
Subject: Re: [R] plotting log regression

Hello,

How can you expect to see the fit line if you are ploting x and y values, not their logarithms?
And your definitions of x and y are wrong, they should use c().

x <- c(1,2,3,4,5)
y <- c(6,7,8,9,10)

plot(log(x), log(y))

fit <- lm(log(y) ~ log(x))  # Same as glm
abline(fit)


Please read R-intro, in the doc folder of your installation of R.

Hope this helps,

Rui Barradas
Em 14-12-2012 13:58, mrkooper escreveu:

I want to plot the regression line of a log regression into a plot 
with my normal, nonlog, data.

for example

x <- (1,2,3,4,5)
y <- (6,7,8,9,10)

plot (x,y)

I tried a log-regression by

a <- glm (log(y) ~ log(x))

and then i tried to insert the answer to my graph, where the standard 
values are shown:
abline (a, col="red")

unfortunately it does not work....




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