Bookmark and Share

Notice: On March 31, it was announced that Statalist is moving from an email list to a forum. The old list will shut down on April 23, and its replacement, statalist.org is already up and running.


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: st: proportional random sampling


From   Steve Nakoneshny <scnakone@ucalgary.ca>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: proportional random sampling
Date   Tue, 25 Oct 2011 11:05:41 -0600

Hi Cam,

We're investigating in a retrospective study whether or not a particular pathologic feature of a tumour can be accurately predicted using an imaging modality (CT scan) prior to surgery. We've identified 44 eligible patients for which the distribution of this feature is approximately 2:1. Prior to undertaking the majority of the work, it was suggested that we take a random sample of each group (positive and negative) and ask the radiologists to asses their scans blindly in order to validate the data collection instrument as a pilot test.

The plan was to go with 5 from each arm, but it was later suggested that we provide them with an unequal distribution so that the radiologists don't automatically assume a 50/50 split. I could easily go with a fully randomized selection, but I want to ensure that we have a representative proportion for each, hence wanting to retain the 2:1 ratio.

I have already narrowed down the dataset to a random sample I'm comfortable with via the code I employed previously. I was simply asking of the list if anyone could suggest an alternate means of arriving at a similar result in perhaps a more elegant fashion as a purely intellectual exercise. If not, that's fine too.

Thanks,
Steve

On 2011-10-24, at 8:51 PM, Cameron McIntosh wrote:

> Steve,
> I think that if you described the motivation for this exercise, it might help elicit advice -- perhaps some that even suggests an alternative way of looking at your problem, whatever that may be. :)
> Thanks,
> Cam
> 
> ----------------------------------------
>> From: scnakone@ucalgary.ca
>> To: statalist@hsphsun2.harvard.edu
>> Date: Mon, 24 Oct 2011 17:15:20 -0600
>> Subject: st: proportional random sampling
>> 
>> Dear Statalisters,
>> 
>> I have a small dataset (n=44) from which I want to draw a random sample of records. The distribution of these records across my variable of interest in approximately 2:1. What I wish to do is to create a random sample of records of size n that retains the proportional distribution across my variable of interest.
>> 
>> Assuming a random sample where n=12, I wrote the following code:
>> 
>> sort ecs
>> by ecs: sample 8,count
>> sample 50 if ecs==1
>> 
>> ------
>> Although how I coded it certainly works, what I am wondering if there is a more elegant means of coding to achieve a similar result?
>> 
>> 
>> Thanks,
>> Steve
>> *
>> * For searches and help try:
>> * http://www.stata.com/help.cgi?search
>> * http://www.stata.com/support/statalist/faq
>> * http://www.ats.ucla.edu/stat/stata/
> 		 	   		  
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/


*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/


© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   Site index