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 <josh...@yahoo.com> 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]] > > ______________________________________________ > R-help@r-project.org 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/ ______________________________________________ R-help@r-project.org 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.