clear

**Make a dataset length of 100***
set obs 100

***MAke a random normal variable x, and an error e***
drawnorm x, mean(4) sd(2)
drawnorm e, sd(7)

***Generate a variable y that is a cubic function of x, with an error***
gen y=5*x-2*x^2+0.5*x^3+e

***Scatter y x**
scatter y x

***Perform a linear regression***
regress y x
predict xb0, xb

***Calculate restricted cubic splines with 1 internal knot placed at 50th centile of x***
rcsgen x, gen(splx) df(2)

**Look at the knot placements***
return list

**Check if the knots are placed as expected***
su x, detail

**Regress y on spline terms***
regress y spl*

***Make predictions**
predict xb1, xb

***Generate restricted cubic spline terms with two internal knots (equally spaced)***
rcsgen x, gen(splx2) df(3)

**Check the knots***
return list

**Regress and predict***
regress y splx2?
predict xb2, xb

**Plot results***
line xb0 xb1 xb2 x, sort|| scatter y x, msize(small) ///
	legend(order(1 "Linear" 2 "1 Internal Knot" 3 "2 Internal Knots"))