October 2017
Beginner to intermediate
572 pages
26h 1m
English
We can illustrate the second order polynomial regression model in the formula, where α is the intercept, while β illustrates regression coefficients.
In the preceding screenshot (step 1), the scatter plot of the x and y2 variables does not fit in a linear relationship, but shows a concave downward curve (or convex upward) with the turning point at x=11. In order to model the nonlinear relationship, we apply the poly function with an argument of 2 to fit the independent x variable and the dependent y2 variable. The red line in the screenshot shows that the model perfectly fits the data.
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