[R] MAD

[deepayan.sarkar at gmail.com]

On 9/18/07, Nair, Murlidharan T <mnair at iusb.edu> wrote:
>
>
> -----Original Message-----
> From: Deepayan Sarkar [mailto:deepayan.sarkar at gmail.com]
> Sent: Monday, September 17, 2007 5:10 PM
> To: Nair, Murlidharan T
> Cc: r-help at stat.math.ethz.ch
> Subject: Re: [R] MAD
>
> On 9/17/07, Nair, Murlidharan T <mnair at iusb.edu> wrote:
> >
> > I am calculating the median absolute deviation using mad function, and
> > it tends to ignore the parameter constant=1, when I am calculating it
> > for x=seq(1:5). Am I missing something here?
> >
> > x<-seq(1:5)
> > mad(x)# gives [1] 1.4826
> > mad(x, constant=1)# gives [1] 1
> > #Here is the long form
> > dev.from.median<-abs((x-median(x)))
> > dev.from.median # Gives [1] 2 1 0 1 2
> > sum(dev.from.median) # Gives [1] 6
> > sum(dev.from.median)/length(x) # Gives [1] 1.2

I'm pretty sure that adding up a bunch of numbers and dividing the
total by the number of numbers qualifies as computing the mean, not
the median.

> > Did I miss anything here?
>
> yes; mad := Median (not mean) absolute deviation (from the median, by
> default).
>
> -Deepayan
>
> Indeed, its median and that what I am calculating in the long form.  So,
> what is that you found I was doing differently? May be I missed your
> point.
> Thx../M
>