# Sample size formulae

Six Sigma – iSixSigma Forums Old Forums General Sample size formulae

Viewing 2 posts - 1 through 2 (of 2 total)
• Author
Posts
• #28276

anon
Participant

I am trying to work out how to derive the formula for sample size for estimating proportions n = (2/d)squared*(p(1-p)) from the formula for estimating averages n= (2s/d)squared.
The formula I have for the standard deviation of the binomial distribution is s = sqrt[p(1-p)/n], but this doesn’t work out. I’m left with an extra n.
Is anyone able to help me with this ? Thanks.

0
#70197

Ken K.
Participant

The ASQ book “How to Choose the Proper Sample Size” by Gary G. Brush gives the following formula (kinda tough in this format):

n = [Z{(1+A)/2] / ARCSIN{(delta/100) / SQRT(PB*(100-PB)/10000)}]
where Z{p} is the z-value for the standard normal distribution that gives a lower tail area of p.
A is the confidence level expressed as a proportion (between 0 & 1)
delta is the desired uncertainty in the estimate of the proportion (think of it as the +/- confidence half interval for p).
PB is the estimated “toward .5” bound for the proportion being estimated.

0
Viewing 2 posts - 1 through 2 (of 2 total)

The forum ‘General’ is closed to new topics and replies.