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Topic: An estimation question
Replies: 5   Last Post: May 2, 2012 10:20 PM

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analyst41@hotmail.com

Posts: 117
Registered: 4/27/05
Re: An estimation question
Posted: Apr 28, 2012 2:42 PM
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On Apr 28, 11:18 am, "analys...@hotmail.com" <analys...@hotmail.com>
wrote:
> This problem occurs a lot in real life..
>
> You sample n people, and a proportion p of them are found to be
> carrying a red flag (like some political party, prefer a brand of soap
> etc.). Textbooks say that the estimate of the proportion carrying the
> red flag in the total population is p with a variance of n.p.(1-p).


correction: variance = p(1-p)/n.

> This would indicate that p close to 0 or 100 pct can be estimated with
> smaller samples than p around 50 pct with the same confidence.
>
> But suppose we have carried out these samplings repeatedly and past
> results show that the proportion carrying the red flag always comes in
> between 0 and say 15 pct.  We can even estimate a histogram
> distribution of p from past samples.  If we now make a new sampling of
> n items - and we wish to rely on the past sampling results, how would
> the mean and variance estimates change?
>
> Thanks for any replies.





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