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Re: st: Loop to compare several variables within different timepoints


From   Nikolaos Pandis <[email protected]>
To   [email protected]
Subject   Re: st: Loop to compare several variables within different timepoints
Date   Sun, 2 Feb 2014 13:29:21 +0200

I completely agree with your  initial comment-this was more of an exercise.
How would the code change if we assume that the exact number of variables is 25?
Thank you,

Nick

On Sun, Feb 2, 2014 at 12:52 PM, Nick Cox <[email protected]> wrote:
> Statistically, this sounds dubious and unsound: the tests are not
> independent and the shotgun approach raises questions about your
> interpretation of the resulting P-values.
>
> Focusing on the Stata question, which is of some wider interest:
>
> If your variables were just a1, a2, a3, ..., c1, c2, c3 you could go
>
> foreach v in a b c {
>       signrank `v'1 = `v'2
>       signrank `v'3 = `v'2
> }
>
> so this just raises the question of how to extend "a b c" to whatever
> stubs you have. Your description of variable names is too vague
> ("about 25 variables") to imply exact code, but this shows one trick:
>
> unab stubs : *1
> local stubs : subinstr local stubs "1" "", all
>
> That would reduce (e.g.)
>
> a1 b1 c1 d1 e1 f1 g1 h1 i1 j1
>
> to
>
> a b c d e f g h i j
>
> after which the code would be
>
> foreach v of local stubs {
>       signrank `v'1 = `v'2
>       signrank `v'3 = `v'2
> }
>
> Nick
> [email protected]
>
>
> On 2 February 2014 10:38, Nikolaos Pandis <[email protected]> wrote:
>> I have about 25 variables for  which I recorded outcomes at 3 times
>> points (t1, t2, t3)
>> I  would like to construct a loop where I can automate testing using
>> the "signrank" test
>>
>> I would like to do the following:
>>
>> signrank a1=a2
>> signrank b1=b2
>> signrank c1=c2
>> .....
>> signrank a3=a2
>> signrank b3=b2
>> signrank c3=c2
>> ..............
>>
>> a,b,c are the variables and 1,2,3 refer to the timepoints
>>
>> I am only interested in 25*2=50 comparisons and not to compare
>> different letter variables between them. Only within the same
>> variables to compare between timepoints.
>>
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