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MathGroup Archive 1999

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Re: quartiles

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18224] Re: [mg18214] quartiles
  • From: David Withoff <withoff at wolfram.com>
  • Date: Thu, 24 Jun 1999 14:24:11 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

> I am working with some statistics problems and have a question about finding
> quartiles for a set of data
> 
> salaries =
> {250000,100000,60000,60000,40000,40000,40000,40000,25000,20000,20000,20000,
>   18000,16000,16000}
> 
> Quartiles[salaries]
> 
> {20000,40000,55000}
> 
> The upper quartile should be the median of the numbers above the median, so
> why is it 55000?
> 250000,100000,60000,
> 60000,
> 40000,40000, 40000
> 
> Does Mathematica use some algorithm to get rid of outliers before finding
> quartiles,  or does it eliminate the median from the data set before finding
> the quartiles, .....?
> 
> The set of data I used as an example was taken from the math text I am using
> and the answer the text supplies, and the answer I think I should get, is
> different from the one Mathematica gets.  I would appreciate any advice on this!
> 
> Tom De Vries

A discussion of the definition of Quartiles, and some alternate definitions,
can be found in

http://support.wolfram.com/Kernel/Symbols/Statistics/DescriptiveStatistics/Quartiles.html

You can also get definitive information about these definitions by looking
in the Statistics`DescriptiveStatistics` package, as the programming is
straightforward.

There are several definitions of quartiles that are in common use.

Dave Withoff
Wolfram Research


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