Re: st: Control groups

[Steven Samuels <sjhsamuels@earthlink.net>]

Alexander,

Without more information, I cannot tell if -samnpsi- or any of the  
other programs that you tried will give you proper answers.  They  
will be okay, for example, if 1) you measure responses without  
sampling or by simple random sampling; and 2) you don't intend to  
generalize your findings beyond the two particular populations you  
study. Different designs other than aimple two-group cross-sectional  
comparison might reduce the needed sample size and strengthen your  
conclusions.  Whether your control group is internal (same  
population) or external (another population) matters, too.

In any case, more details would be helpful.

Steven

On May 9, 2008, at 5:52 PM, <Alexander.Severinsen@telenor.com>  
<Alexander.Severinsen@telenor.com> wrote:


> Dear Statalisters,
>
> Say I have a population of 500 000. I would like to treat this
> population with some sort of communication, and to be able to measure
> the effect of this treatment I have the opportunity to draw a control
> group. Based on earlier experiences the effects between the treated  
> and
> the controlgroup could be as small as 0.5%.
>
> I want to be able to detect such a small effects, and I am  
> wondering how
> large my control groups ideally would be to track these changes,  
> say at
> an alpha level of 0.05.
>
> I have tried to use the fpower (findit fpower) and the simpower  
> (findit
> simpower) to determine optimal control group sizes. I am curious  
> whether
> there are other alternatives in Stata?
>
> Thanks! And have a nice weekend.
>
> Best wishes,
> Alexander
>
> *
> *   For searches and help try:
> *   http://www.stata.com/support/faqs/res/findit.html
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/
*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/