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MathGroup Archive 2006

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Re: Draw approximated normal distribution based on mean, median, percentiles?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg70122] Re: [mg70092] Draw approximated normal distribution based on mean, median, percentiles?
  • From: leigh pascoe <leigh at cephb.fr>
  • Date: Wed, 4 Oct 2006 05:59:38 -0400 (EDT)
  • References: <200610031016.GAA06382@smc.vnet.net>

rflaaten at start.no wrote:
> Hello all,
>
> I searched the forum for any info on this, so here goes.
>
> I need to reference some statistical data from a study. The information
> given there for an age distribution is: mean, standard deviation,
> median plus the 25th and 75th percentiles. Now, I have tried in vain to
> get Excel or SPSS to draw this for me. Is there any way of inputting
> percentiles and median into Mathematica? The normal distribution
> function only takes mean and sd as far as I know.
>
>
> Any help would be much appreciated.
> Richard
>
>
>
>   
Let me start by saying I don't know the answer to your question, so you 
can ignore what is below if you like.

If the distribution is Normal the mean and variance (or standard 
deviation) are sufficient to define it. In this case the median is the 
same as the mean and the percentiles are symmetrical about the mean. 
However an age distribution is unlikely to be Normal and depends on the 
prior state of the population, the birth process and the time to failure 
(or death). Perhaps this is why you are given  extra parameters 
reflecting the assymmetry and  kurtosis. You are probably better off 
drawing a histogram of the numbers (or proportion) in each age class.

What do you want to do with your distribution once you have it?

LP


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