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.