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Re: st: How do I demonstrate that a sample is randomly drawn from a population?


From   Nick Cox <njcoxstata@gmail.com>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: How do I demonstrate that a sample is randomly drawn from a population?
Date   Mon, 15 Apr 2013 00:45:32 +0100

I agree with David. Randomness of sampling has to be judged by knowing
how the sample was actually generated.

A quantile-quantile plot is the best way to keep track of the
similarities or differences between sample and population, in my view.
Nick
njcoxstata@gmail.com


On 14 April 2013 22:14, Yuval Arbel <yuval.arbel@gmail.com> wrote:
> David, thanks for your answer. As I noted in my question - I already
> tried the difference-of-mean test. I'm not sure, however, this is the
> appropriate test for the problem I presented (in your answer - you
> said the same thing in different words).
>
> My educated guess would be - that to demonstrate a random sample - I
> need to make some comparison between the population and sample
> distribution. The question would still be what exact test do I need -
> and what is the appropriate command in stata
>
> On Sun, Apr 14, 2013 at 1:56 PM, David Greenberg <dg4@nyu.edu> wrote:
>> Testing whether the mean of a sample is significantly different from the
>> mean of a population is a topic covered in every introductory statistics
>> book. However, even if the differences in means is not statistically
>> significant,  you still have not demonstrated that the sample was, in fact,
>> randomly drawn from the given population. David Greenberg, Sociology
>> Department, New York University
>>
>>
>> On Sun, Apr 14, 2013 at 3:00 PM, Yuval Arbel <yuval.arbel@gmail.com> wrote:
>>>
>>> Dear statalisters,
>>>
>>> I have two files:
>>>
>>> 1) The first file contains the grades of all population of Open
>>> University students.
>>>
>>> 2) The second file contains the grades of Open University students,
>>> who filled a questionnaire via the net.
>>>
>>> I would like to show that the second file is a random sample drawn
>>> from the first file.
>>>
>>> The question is can I provide a statistical evidence that the sample
>>> is indeed random? what are the appropriate commands in stata?
>>>
>>> P.S. I thought to run the test of difference of means between two
>>> populations. Having reconsidered, however, I'm not talking here about
>>> two populations, but rather a sample,which is drawn from a given
>>> population.
>>>
>>> As always, your answers will be very much appreciated
>>>
>>> --
>>> Dr. Yuval Arbel
>>> School of Business
>>> Carmel Academic Center
>>> 4 Shaar Palmer Street,
>>> Haifa 33031, Israel
>>> e-mail1: yuval.arbel@carmel.ac.il
>>> e-mail2: yuval.arbel@gmail.com
>>> *
>>> *   For searches and help try:
>>> *   http://www.stata.com/help.cgi?search
>>> *   http://www.stata.com/support/faqs/resources/statalist-faq/
>>> *   http://www.ats.ucla.edu/stat/stata/
>>
>>
>
>
>
> --
> Dr. Yuval Arbel
> School of Business
> Carmel Academic Center
> 4 Shaar Palmer Street,
> Haifa 33031, Israel
> e-mail1: yuval.arbel@carmel.ac.il
> e-mail2: yuval.arbel@gmail.com
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
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> *   http://www.ats.ucla.edu/stat/stata/
*
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