##
Proportion Difference Power / Sample Size Calculation

(Revised 10/30/2009 - Also display results of uncorrected ("classical")
calculation.)

This screen computes the sample size required to detect a difference between
two proportions.
Note: Before using this page for the first time, make sure you read the
JavaStat user interface guidelines for important
information about interacting with JavaStat pages.

**Note: **This page incorporates a continuity
correction to the usual sample-size formula based on the normal approximation
to the binomial distribution. This correction increases the sample size (for
each group) by an amount approximately equal to 2/abs(p1-p2), where p1 and
p2 are the population proportions for the two groups. For a good discussion
of this, see: *Statistical Methods for Rates and Proportions* by Joseph
L. Fleiss (2^{nd} ed., 1981, John Wiley & Sons, NY), chapter
3. This web page produces values consistent with those in Table A3 of that
book.

Return to the Interactive Statistics page or to
the JCP Home Page

Send e-mail to John C. Pezzullo at