Page 357 - Applied Statistics with R

14.2. PREDICTOR TRANSFORMATION 357

coef(lm(y ~ x + I(x ^ 2), data = quad_data))

## (Intercept) x I(x^2)
## 3.0649446 -0.5108131 5.0739805

coef(lm(y ~ x + x:x, data = quad_data))

## (Intercept) x
## -18.32715 24.87163

coef(lm(y ~ x * x, data = quad_data))

## (Intercept) x
## -18.32715 24.87163

coef(lm(y ~ x ^ 2, data = quad_data))

## (Intercept) x
## -18.32715 24.87163

coef(lm(y ~ x + x ^ 2, data = quad_data))

## (Intercept) x
## -18.32715 24.87163

coef(lm(y ~ I(x + x), data = quad_data))

## (Intercept) I(x + x)
## -18.32715 12.43582

coef(lm(y ~ x + x, data = quad_data))

## (Intercept) x
## -18.32715 24.87163

14.2.7 Data Example