[GRASS-dev] Re: [GRASS GIS] #474: r.quantile: segfaults with percentile=100

[Michael Barton]

On Feb 12, 2009, at 10:00 AM, <grass-dev-request at lists.osgeo.org> <grass-dev-request at lists.osgeo.org 
 > wrote:

> Date: Wed, 11 Feb 2009 21:34:18 +0000
> From: Glynn Clements <glynn at gclements.plus.com>
> Subject: Re: [GRASS-dev] Re: [GRASS GIS] #474: r.quantile: segfaults
> 	with	percentile=100
> To: dylan.beaudette at gmail.com
> Cc: grass-dev at lists.osgeo.org
> Message-ID: <18835.17498.645317.388349 at cerise.gclements.plus.com>
> Content-Type: text/plain; charset=us-ascii
>
>
> Dylan Beaudette wrote:
>
>>> It's intended so that quant=N gives "N-tiles", e.g. quant=4 gives
>>> quartiles, quant=10 gives deciles, etc. AIUI, the convention is  
>>> not to
>>> include the endpoints, e.g. "quartiles" are given as 25%, 50%, and  
>>> 75%.
>>
>> Is this a convention? I am not a math/stats expert, but in R I see  
>> that the
>> convetion is to report it like this:
>>
>> # generate some random data
>> x <- rnorm(100)
>> # compute quartiles:
>> quantile(x)
>>        0%        25%        50%        75%       100%
>> -2.1691897 -0.3627331  0.1307290  0.6652009  2.4798260
>>
>> # we can see that it includes the min/max:
>> summary(x)
>>    Min.  1st Qu.   Median     Mean  3rd Qu.     Max.
>> -2.16900 -0.36270  0.13070  0.07639  0.66520  2.48000
>>
>> Is this just a display/semantics thing?
>
> I don't have a statistics background, but I'm more familiar with
> seeing e.g. 1st, 2nd, and 3rd quartiles, without the 0th and 4th
> quartiles.
>
> I can add the 0th and Nth quantiles if desired (i.e. quant=N gives N+1
> values).

I agree with Glynn. I don't see the 0 and Nth quartile referred to.  
They are simply the min and max, which seem easier for most people to  
understand too.

Michael