From jorismeys at gmail.com  Wed May 31 16:40:30 2017
From: jorismeys at gmail.com (Joris Meys)
Date: Wed, 31 May 2017 16:40:30 +0200
Subject: [Rd] stats::line() does not produce correct Tukey line when n
 mod 6 is 2 or 3
In-Reply-To: <CAO1zAVa3=dA_atBNxj9kAX_Rh=5pCMiLK7BAuwq9hhY6KACQag@mail.gmail.com>
References: <CAN7_cLjefc605D1ATS__MOV4gN7fKDBo5Nx_CNB_B9cDbAxc6w@mail.gmail.com>
 <ffc3e473-622d-796f-a06a-6e1f92f8ab5f@gmail.com>
 <CAN7_cLjmQFtZf9z-qJKdWRCaRY2uxfP8k5=QJsptz3U+TtP8oA@mail.gmail.com>
 <CAN7_cLjbz6S8u79jtx52XgfD1LcpO8CePYUhrunYqrzXHMMN8A@mail.gmail.com>
 <024A7E7D-45F8-4C95-A9BD-DBEB1D085BFA@gmail.com>
 <94b65a5b-da9e-ec5c-e428-7c5dbf175ec1@insa-toulouse.fr>
 <8c167bbb-130d-3798-a9e8-24c4377db313@insa-toulouse.fr>
 <d10ebb8c-0c49-5b0e-5b3c-b06073bfe447@insa-toulouse.fr>
 <22829.8246.695545.320438@stat.math.ethz.ch>
 <396781eb-1712-aa54-96f2-a6c4df0284f4@insa-toulouse.fr>
 <22829.41724.818300.640880@stat.math.ethz.ch>
 <c9af2c00-3653-29f8-7c6a-5a08d6de498e@insa-toulouse.fr>
 <CAO1zAVb8faubH7FrBfsx8c04xsZce2p2Ei9NaBELrfn2Q8JMEA@mail.gmail.com>
 <055b3d48-5f94-d087-74b8-b511e6c45baf@insa-toulouse.fr>
 <CAO1zAVa3=dA_atBNxj9kAX_Rh=5pCMiLK7BAuwq9hhY6KACQag@mail.gmail.com>
Message-ID: <CAO1zAVbeDxrQkD3f+ndMEfFyca2eYuUwt0cCV0kh4xb3N2EH2Q@mail.gmail.com>

And with "equally spaced" I obviously meant "of equal size". It's getting
too hot in the office here...

On Wed, May 31, 2017 at 4:39 PM, Joris Meys <jorismeys at gmail.com> wrote:

> Seriously, if a method gives a wrong result, it's wrong. line() does NOT
> implement the algorithm of Tukey, even not after the patch. We're not
> discussing Excel here, are we?
>
> The method of Tukey is rather clear, and it is NOT using the default
> quantile definition from the quantile function. Actually, it doesn't even
> use quantiles to define the groups. It just says that the groups should be
> more or less equally spaced. As the method of Tukey relies on the medians
> of the subgroups, it would make sense to pick a method that is
> approximately unbiased with regard to the median. That would be type 8
> imho.
>
> To get the size of the outer groups, Tukey would've been more than happy
> enough with a:
>
> > floor(length(dfr$time) / 3)
> [1] 6
>
> There you have the size of your left and right group, and now we can
> discuss about which median type should be used for the robust fitting.
>
> But I can honestly not understand why anyone in his right mind would
> defend a method that is clearly wrong while not working at Microsoft's
> spreadsheet department.
>
> Cheers
> Joris
>
> On Wed, May 31, 2017 at 4:03 PM, Serguei Sokol <sokol at insa-toulouse.fr>
> wrote:
>
>> Le 31/05/2017 ? 15:40, Joris Meys a ?crit :
>>
>>> OTOH,
>>>
>>> > sapply(1:9, function(i){
>>> +   sum(dfr$time <= quantile(dfr$time, 1./3., type = i))
>>> + })
>>> [1] 8 8 6 6 6 6 8 6 6
>>>
>>> Only the default (type = 7) and the first two types give the result
>>> lines() gives now. I think there is plenty of reasons to give why any of
>>> the other 6 types might be better suited in Tukey's method.
>>>
>>> So to my mind, chaning the definition of line() to give sensible output
>>> that is in accordance with the theory, does not imply any inconsistency
>>> with the quantile definition in R. At least not with 6 out of the 9
>>> different ones ;-)
>>>
>> Nice shot.
>> But OTOE (on the other end ;)
>> > sapply(1:9, function(i){
>> +   sum(dfr$time >= quantile(dfr$time, 2./3., type = i))
>> + })
>> [1] 8 8 8 8 6 6 8 6 6
>>
>> Here "8" gains 5 votes against 4 for "6". There were two defector methods
>> that changed the point number and should be discarded. Which leaves us
>> with the score 3:4, still in favor of "6" but the default method should
>> prevail
>> in my sens.
>>
>> Serguei.
>>
>
>
>
> --
> Joris Meys
> Statistical consultant
>
> Ghent University
> Faculty of Bioscience Engineering
> Department of Mathematical Modelling, Statistics and Bio-Informatics
>
> tel :  +32 (0)9 264 61 79 <+32%209%20264%2061%2079>
> Joris.Meys at Ugent.be
> -------------------------------
> Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php
>



-- 
Joris Meys
Statistical consultant

Ghent University
Faculty of Bioscience Engineering
Department of Mathematical Modelling, Statistics and Bio-Informatics

tel :  +32 (0)9 264 61 79
Joris.Meys at Ugent.be
-------------------------------
Disclaimer : http://helpdesk.ugent.be/e-maildisclaimer.php

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[Rd] stats::line() does not produce correct Tukey line when n mod 6 is 2 or 3
Joris Meys