How to Estimate a Polynomial Regression Model in R (Example Code)

This tutorial shows how to fit a polynomial regression model in R programming.

Creation of Example Data

data(iris)                                            # Iris flowers as example data
head(iris)
#   Sepal.Length Sepal.Width Petal.Length Petal.Width Species
# 1          5.1         3.5          1.4         0.2  setosa
# 2          4.9         3.0          1.4         0.2  setosa
# 3          4.7         3.2          1.3         0.2  setosa
# 4          4.6         3.1          1.5         0.2  setosa
# 5          5.0         3.6          1.4         0.2  setosa
# 6          5.4         3.9          1.7         0.4  setosa

Example: Fitting Third Order Polynomial Using poly() Function

lm(Sepal.Length ~ poly(Sepal.Width, 3), data = iris)  # Use orthogonal polynomials
# Call:
# lm(formula = Sepal.Length ~ poly(Sepal.Width, 3), data = iris)
# 
# Coefficients:
#           (Intercept)  poly(Sepal.Width, 3)1  poly(Sepal.Width, 3)2  poly(Sepal.Width, 3)3  
#                 5.843                 -1.188                 -1.416                  1.923

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