[R] MAD

[Nair, Murlidharan T]

-----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
> # The long form does not match the output from the function
>
> # When x<-seq(1:10) they match
> x<-seq(1:10)
> dev.from.median<-abs((x-median(x)))
> sum(dev.from.median)/length(x) # Gives 2.5
> mad(x, constant=1) # Gives 2.5
> #The long form matches the output from the function
>
> 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