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rscale

Why does scale center=F change the mean?

As the title says, how does the following come about:

set.seed(1)  # for reproducibility
x <- rnorm(30, 10, 2)

mean(x)
# [1] 10.16492
mean(scale(x, center=FALSE))
# [1] 0.9678482
Solution

  • ?scale explains all: "scaling is done by dividing the (centered) columns of x by their standard deviations if center is TRUE, and the root mean square otherwise."

    We can show that scaling by the RMS is what actually happened:

    rms = sqrt(sum(x^2)/(length(x)-1))
mean(x)/rms
# [1] 0.9678482