trimmed mean in R seems to round the trimming fraction
VINOD at FORDHAM.EDU wrote:
subject: trimmed mean in R seems to round the trimming fraction to r-help at stat.math.ethz.ch. Consider the following example of 10 numbers. 10% trimmed mean is correct but you can see that the result is the same for many trimming fractions till 0.20! For example 13% trimmed mean should use interpolation of second and eighth ordered observation. R does not seem to do this. The correct 13% trimmed mean is the average of 7.4 middle observations (28+46+50+52+54+63+82+64.4)/7.4 Answer=(439.4)/7.4= 59.3784
z=c(23, 40, 46, 50, 52, 54, 63, 82,92,98) mean(z, trim=0.10)
[1] 59.875
mean(z, trim=0.13) # wrong result is 59.875
[1] 59.875
mean(z, trim=0.15)
[1] 59.875
mean(z, trim=0.18)
[1] 59.875
mean(z, trim=0.1999999)
[1] 59.875
mean(z, trim=0.20)
[1] 57.83333
mean(z, trim=0.40)
[1] 53
Hi,
The "trim" argument works as documented. Did you read ?mean:
If 'trim' is non-zero, a symmetrically trimmed mean is computed
with a fraction of 'trim' observations deleted from each end
before the mean is computed.
Also, I don't recall ever learning your method for trimmed mean, but R
is a programming language and you can always write your own trimmed mean
function.
HTH,
--sundar