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Re: st: CDF plot with normal probability axis
From
Nick Cox <[email protected]>
To
"[email protected]" <[email protected]>
Subject
Re: st: CDF plot with normal probability axis
Date
Thu, 14 Nov 2013 13:18:53 +0000
My point is just that I underline that there is a choice and refer to
literature that explains the choices. As a hydrologist, or rather as
someone who publishes in hydrological journals, I am drawn to (i -
0.5)/n which is what the engineering hydrologist Allen Hazen used in
1914, as something easy to teach and which works fine for me. As a
Stata user-programmer, I let people choose.
Nick
[email protected]
On 14 November 2013 13:10, David Hoaglin <[email protected]> wrote:
> Thanks, Nick.
>
> I didn't see a = 1/3 in the FAQ or the SJ articles, and the derivation
> of it is interesting.
>
> I agree that small differences in plotting position are unlikely to
> make much difference.
>
> You make a good argument for avoiding -qnorm- and -quantile-.
>
> David Hoaglin
>
> On Thu, Nov 14, 2013 at 7:54 AM, Nick Cox <[email protected]> wrote:
>> Quite so. Choice of plotting position is discussed at some length in
>> the FAQ I mentioned, which links to the literature, and in
>> publications on my -qplot- and its predecessor -quantil2- in the SJ
>> and STB respectively.
>>
>> Naturally I am all in favour of using a better method rather than a
>> weaker one, but I remain unconvinced that minute differences in
>> plotting position either are discernible on a graph or have impact on
>> decisions about data, so long as you are not working with very small
>> samples. If you are, nothing much helps.
>>
>> Your bigger argument is with StataCorp, who wire i / (n + 1) into
>> -qnorm- and (i - 0.5) / _N into -quantile- and don't allow variations.
>> My quantile plotting programs have always allowed user choice of a in
>> (i - a) / (n - 2a + 1).
>>
>> Nick
>> [email protected]
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