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Topic: Confidence interval for p
Replies: 4   Last Post: Apr 10, 1997 9:41 AM

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 DougKuhlmann-PhillipsAcademy-Math Posts: 119 Registered: 12/6/04
Confidence interval for p
Posted: Apr 9, 1997 6:16 PM

Yet another thought on using the normal approximation to find a confidence
for p when we technically don't know the standard deviation (since we need
to know p to know the standard deviation):

Consider the variance for one binomial trial: p(1-p). Regardless of the
true value of p, we do know that p(1-p)<=1/4. Hence if we replace p(1-p)
with 1/4 we will error by possibly making the standard deviation (of the
number of trials or of the proportion) too big. That will have the effect
of making our confidence intervals larger than they might have to be. I.E.
we will error on the side of caution.

Doug

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Doug Kuhlmann (508)-749-4242