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# Re: st: Unique Randomization within groups

 From Jonah Rexer To statalist@hsphsun2.harvard.edu Subject Re: st: Unique Randomization within groups Date Thu, 31 Jan 2013 15:37:11 +0300

```I tried that before, but I can't set an obs lower than 99 on my
version of stata. Is this normal?

On Thu, Jan 31, 2013 at 3:25 PM, Nick Cox <njcoxstata@gmail.com> wrote:
> Abstracting from the complicated context
>
> clear
> set obs 3
> set seed <whatever>
> gen y = runiform()
> sort y
> gen wanted = _n
>
> gives you -wanted- that is 1, 2, 3. Which observations are assigned 1,
> 2, 3 is random by virtue of shuffling according to previously
> generated random numbers. So use the sort order, not the random
> numbers themselves.
>
> (There still is a minute probability of ties. I wouldn't expect that
> to bite in practice.)
>
> On Thu, Jan 31, 2013 at 12:14 PM, Jonah Rexer <jorexer@gmail.com> wrote:
>> Hello,
>>
>> I am doing a randomization among 3 groups (2 treatment and 1 control) for a
>> micro experiment.
>> Our sample is small, N=99 with the unit being a cluster (a group of 2-3
>> respondents).
>> I have merged clusters to assign each a random number. But instead of
>> stratifying, since our sample is so small, I have organized each cluster
>> into a group of 3 clusters (so 33 groups, each with 3 clusters) based on
>> our stratification variables.
>>
>> What I want to do is assign a random integer, 1-3, within each group. I've
>> used the command:
>>
>> set seed 4109
>>
>> bysort cluster_group : gen random1=floor((3-1+1)*runiform()+1)
>>
>> The problem is that this doesn't give me a unique number. Within each
>> group, i need one observation (cluster) to be 1, one to be 2, and one to be
>> 3. This is why I used bysort, but it doesn't seem to be making any
>> difference. Is there any way to ensure that the number assigned is unique
>> within the group?
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--
Jonah Rexer
Research Fellow
BRAC Uganda
Plot 90, Busingiri Zone, Nyanama
Kampala, Uganda
www.brac.net
*
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