How do I plot a quadratic regression in R?
The following code generates a qudaratic regression in R.
lm.out3 = lm(listOfDataFrames1$avgTime ~ listOfDataFrames1$betaexit + I(listOfDataFrames1$betaexit^2) + I(listOfDataFrames1$betaexit^3))
summary(lm.out3)
Call:
lm(formula = listOfDataFrames1$avgTime ~ listOfDataFrames1$betaexit +
I(listOfDataFrames1$betaexit^2) + I(listOfDataFrames1$betaexit^3))
Residuals:
Min 1Q Median 3Q Max
-14.168 -2.923 -1.435 2.459 28.429
Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 199.41 11.13 17.913 < 2e-16 ***
listOfDataFrames1$betaexit -3982.03 449.49 -8.859 1.14e-12 ***
I(listOfDataFrames1$betaexit^2) 32630.86 5370.27 6.076 7.87e-08 ***
I(listOfDataFrames1$betaexit^3) -93042.90 19521.05 -4.766 1.15e-05 ***
---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
Residual standard error: 7.254 on 63 degrees of freedom
Multiple R-squared: 0.9302, Adjusted R-squared: 0.9269
F-statistic: 279.8 on 3 and 63 DF, p-value: < 2.2e-16
But how to make a graph of a curve on a graph, I am confused.
To get a graph:
plot(listOfDataFrames1$avgTime~listOfDataFrames1$betaexit)
But the curve?
Is it possible to do this without manually copying the values? As mso suggested, although it works.
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This should work.
# not tested
lm.out3 = lm(avgTime ~ poly(betaexit,3,raw=TRUE),listofDataFrames3)
plot(avgTime~betaexit,listofDataDFrames3)
curve(predict(lm.out3,newdata=data.frame(betaexit=x)),add=T)
Since you didn't provide any data, here's a working example using the built-in mtcars dataset.
fit <- lm(mpg~poly(wt,3,raw=TRUE),mtcars)
plot(mpg~wt,mtcars)
curve(predict(fit,newdata=data.frame(wt=x)),add=T)
Some notes:
(1) It is really a bad idea to refer to external data structures in an argument formula=...
to lm(...)
. Instead, the pivot columns of the data=...
dataframe that are referenced in the argumennt as above and as @mso points out.
(2) You can specify the formula as @mso, or you can use the function poly(...)
with raw=TRUE
.
(3) The function curve(...)
takes an expression as its first argument. This expression must have a variable x
that will be automatically filled with values from the x-axis of the graph. So in this example the expression:
predict(fit,newdata=data.frame(wt=x))
which uses predict(...)
for a model with a dataframe having wt
(predictor variable) given x
.
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