the standard error for your sample percentage is =
sqrt(((100-percentage)*percentage)/n-1)

assume 50% is in A1, 16 in B1

= sqrt(((100%-A1)*A1)/(B1-1))

This comes out to 12.91%

assuming your percentage is normally distributed, then a 95% confidence
interval says you should go +/- 1.96 standard errors from the mean

50% - (1.96 * 12.91%) as the lower bound and

50% + (1.96 * 12.91%) as the upper bound


(1.96 * 12.91%) = 25.303%

so you lower bound formula would be

= A1-1.96*sqrt(((100%-A1)*A1)/(B1-1))
your upper bound formula would be
= A1+1.96*sqrt(((100%-A1)*A1)/(B1-1))

--
Regards,
Tom Ogilvy


Heather Rabbitt wrote in message
om...
Hi,

I'm looking for a formula in excel to give me the maximum and minimum
margin of error at the 95% confidence interval for a given percentage
and sample size.

For example the percentage may be 50% I have a sample size of 16 and
using a stat testing program (STATCHCK) I know the margin of error is
+/- 25% so my maximum would be 75% and my minimum would be 25%.

My problem is I have over 10,000 numbers to check and I want to
automate this in excel. I know there is a data analysis add in excel
but not sure if it can be used to solve my problem.

Any help with my problem would be greatly appreciated.

If you think this should be posted somewhere else please let me know.

Thanks in advance,

Heather