Data Analysis with R statistical Software: A Guidebook for Scientists by and the Guidebook Development Team & Thomas Rob

Author:and the Guidebook Development Team & Thomas, Rob [and the Guidebook Development Team]
Language: eng
Format: epub
Publisher: Eco-Explore CIC
Published: 2015-08-30T16:00:00+00:00

Polynomial regression (parametric non-linear regression)

To fit a curved line to your data, there are two main options: (i) polynomial regression , which uses the square, cube, etc. of your independent variables, or (ii) generalised additive models (GAMs) . The main difference between these two approaches is that polynomial regression uses standard parametric terms to model the data, whereas GAMs use non-parametric “smoothers” to model the data.

To run a polynomial regression, for example with a linear term (x), a quadratic term (x 2 ) and a cubic term (x 3 )

model1 <- lm (y ~ x + I(x^2) + I(x^3))

Note that the letter “I ” (meaning “as is”) is used to prevent R reading what follows as a formula.

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