# [R] how do I plot a regression curve with the data?

Peter Ehlers ehlers at ucalgary.ca
Wed Oct 28 07:57:48 CET 2009

```Ken Ervin wrote:
> I have a data set of 6 or so ordered pairs, and I've been able to graph
> them and have decided to use a high-order polynomial regression.  I've
> used the following piece of code:
>
> regression <- function(x,y) {
>    x <- c(insert_numbers_here)
>    y <- c(insert_other_numbers_here)
>    fit <- lm(y ~ x + I(x^2) + I(x^3) + I(x^4) + I(x^5) + I(x^6) + I(x^7)
> + I(x^8) + I(x^9))
>    summary(fit)
>
> This gives me the coefficients for the regression very nicely, but I
> would like to plot both the data and the regression curve together.  How
> do I plot that regression curve as a function, and can I put it on the
> same set of axes as my data scatter plot?
>
Are you sure that fitting such a high-degree polynomial makes
sense? Is there any theory to support the model? If you really
want to do this, then use predict.lm():

## with xmin, xmax as the limits of your scatterplot
xx <- seq(xmin, xmax, length=51)
yy <- predict(fit, newdata=list(x=xx))
lines(xx, yy)  ## add to scatterplot

-Peter Ehlers

>
> -KE
>
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