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

[Nikolaos Pandis <nikpandis@gmail.com>]

Nick,
Excellent. It worked beautifully!
Thank,
Nick

On Sun, Feb 2, 2014 at 1:34 PM, Nick Cox <njcoxstata@gmail.com> wrote:
> My code makes no assumptions about the exact number of variables, so
> it would not change.
>
> Nick
> njcoxstata@gmail.com
>
>
> On 2 February 2014 11:29, Nikolaos Pandis <nikpandis@gmail.com> wrote:
>> 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 <njcoxstata@gmail.com> 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
>>> njcoxstata@gmail.com
>>>
>>>
>>> On 2 February 2014 10:38, Nikolaos Pandis <nikpandis@gmail.com> 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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