I need a little help here - 2 questions
I need a formula to determine the sample size required to detect a change in proportion. I use n=Z2pq/h2. (h = half interval width)
However, I cannot replicate ny answers on either minitab or SPCXL.
e.g. Manufacturing components with a historical pass rate of say 50%. What sample size do I need to be 95% confident that the pass rate has improved to 55%.
For the difference between 2 sample proportions, what formula can you use to determine sample sizes for a 5% difference at 95% confidence?