Hi Josh,

This is by no means the fanciest solution ever, but as there are

predict methods for many types of models in R, I thought I would show

it this way.

## fit the model

model <- lm(probability ~ poly(temperature, 2), data = x)

## create line values

dat <- data.frame(temperature = seq(min(x$temperature, na.rm = TRUE),

max(x$temperature, na.rm = TRUE), by = .01))

## add predicted y values

dat$yhat <- predict(model, dat)

## plot data

plot(probability ~ temperature, data = x)

## add predicted line

lines(x = dat$temperature, y = dat$yhat, type = "l")

Hope this helps,

Josh

On Mon, Apr 11, 2011 at 12:29 PM, Josh B <

[hidden email]> wrote:

> Dear Listserv,

>

> Here is my latest in a series of simple-seeming questions that dog me.

>

> Consider the following data:

>

> x <- read.table(textConnection("temperature probability

> 0.11 9.4

> 0 2.3

> 0.38 8.7

> 0.43 9.2

> 0.6 15.6

> 0.47 8.7

> 0.09 12.8

> 0.11 9.4

> 0.01 7.7

> 0.83 8

> 0.65 9.3

> 0.05 7.4

> 0.34 10.1

> 0.02 4.8

> 0.07 9.1

> 0.6 15.6

> 0.01 8.4

> 0.9 9.6

> 0.83 8

> 0.12 8.4

> 0.01 8

> 0 5

> 0.11 9.7

> 0.41 7.4

> 0.05 9.4

> 0.09 8.3

> 0 6.1

> 0.12 8.4

> 0.73 7.8

> 0 4.2"), header = TRUE, as.is = TRUE)

> closeAllConnections()

>

> I modeled the relationship: Probability = f(Temperature), i.e., probability as a

> function of temperature.

>

> I found that there is a significant quadratic term in the model:

>

> summary(lm(x[,2] ~ x[,1] + I(x[,1]^2)))

>

> Now the question is: how do I plot it?

>

> I can do this:

> plot(x[,2] ~ x[,1])

>

> ...but I would also like to add a line corresponding to the quadratic function.

> In other words, I want to visually show the relationship among the variables

> that is being modeled. How do I do it? I think the curve() command will be used,

> but I don't know how to employ it.

>

> Thanks very much in advance.

>

> Sincerely,

> -----------------------------------

> Josh Banta, Ph.D

> Center for Genomics and Systems Biology

> New York University

> 100 Washington Square East

> New York, NY 10003

> Tel: (212) 998-8465

>

http://plantevolutionaryecology.org> [[alternative HTML version deleted]]

>

> ______________________________________________

>

[hidden email] mailing list

>

https://stat.ethz.ch/mailman/listinfo/r-help> PLEASE do read the posting guide

http://www.R-project.org/posting-guide.html> and provide commented, minimal, self-contained, reproducible code.

>

--

Joshua Wiley

Ph.D. Student, Health Psychology

University of California, Los Angeles

http://www.joshuawiley.com/______________________________________________

[hidden email] mailing list

https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide

http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.