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