Question

I have a explanatory variable that is centered using scale() that is used to predict a response variable:

d <- data.frame(
  x=runif(100),
  y=rnorm(100)
)

d <- within(d, s.x <- scale(x))

m1 <- lm(y~s.x, data=d)

I’d like to plot the predicted values, but using the original scale of x rather than the centered scale. Is there a way to sort of backtransform or reverse scale s.x?

Thanks!

Answer 1

Take a look at:

attributes(d$s.x)

You can use the attributes to unscale:

d$s.x * attr(d$s.x, 'scaled:scale') + attr(d$s.x, 'scaled:center')

For example:

> x <- 1:10
> s.x <- scale(x)

> s.x
            [,1]
 [1,] -1.4863011
 [2,] -1.1560120
 [3,] -0.8257228
 [4,] -0.4954337
 [5,] -0.1651446
 [6,]  0.1651446
 [7,]  0.4954337
 [8,]  0.8257228
 [9,]  1.1560120
[10,]  1.4863011
attr(,"scaled:center")
[1] 5.5
attr(,"scaled:scale")
[1] 3.02765

> s.x * attr(s.x, 'scaled:scale') + attr(s.x, 'scaled:center')
      [,1]
 [1,]    1
 [2,]    2
 [3,]    3
 [4,]    4
 [5,]    5
 [6,]    6
 [7,]    7
 [8,]    8
 [9,]    9
[10,]   10
attr(,"scaled:center")
[1] 5.5
attr(,"scaled:scale")
[1] 3.02765