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MathGroup Archive 1999

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quartiles

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18214] quartiles
  • From: "Tom De Vries" <tdevries at shop.westworld.ca>
  • Date: Tue, 22 Jun 1999 20:41:10 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Hello !

I am working with some statistics problems and have a question about finding
quartiles for a set of data

Load in the package


Needs["Statistics`DescriptiveStatistics`"]


create a set of data

salaries =
{250000,100000,60000,60000,40000,40000,40000,40000,25000,20000,20000,20000,
  18000,16000,16000}

ask for the quartiles

Quartiles[salaries] 

and this is the response
{20000,40000,55000}

At this point I am probably revealing my ignorance of statistics....   


250000,100000,60000,60000,40000,40000, 40000
40000,  Median
25000,20000,20000,20000,18000,16000,16000

The lower quartile is the median of the values below the median, which I get
with Mathematica 
25000,20000,20000,
20000,
18000,16000,16000

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!

Thanks!

Tom De Vries



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