Sample Size for a Population Proportion


This Webulator is based on the following sample size formula for proportions

Conversion table for percent confidence to Z
90% [Zalpha] = 1.64 91% [Zalpha] = 1.70
92% [Zalpha] = 1.75 93% [Zalpha] = 1.81
94% [Zalpha] = 1.88 95% [Zalpha] = 1.96
96% [Zalpha] = 2.05 97% [Zalpha] = 2.17
98% [Zalpha] = 2.33 99% [Zalpha] = 2.58

Only enter the numeric values without special characters for the initial population, the expected proportion, the Zalpha for the percent confidence, and the percent error, in the appropriate Webulator cells and then click on the button labelled CALCULATE to compute the sample size required to represent a proportion of a population.

Initial population Expected proportion Zalpha for the
percent confidence
Percent error
Sample Size Numerator Denominator

Computations for Sample Size are discussed in several texts including:

--Hirsch, R.P., and Riegelman, R.K., Statistical First Aid: Interpretation of Health Research Data, Boston, Blackwell Scientific Publications, page 73-75,1992.
-- Knapp R.G., and Miller, M.C., Clinical Epidemiology and Biostatistics , Baltimore, Williams and Wilkins, 1992.

--Fleiss, J., (1981). Statistical methods for rates and proportions, (2nd ed). Toronto: John Wiley and Sons.
-- Freedman, D., Pisani, R., Purves, R., Adhikari, A., (1991). Statistics. New York: Norton and Company.
--Freund, J.E., and Simon, G.A., Statistics A First Course, New Jersey, Prentice Hall, page 66-67,1991.
--Saunders, D.H., Statistics A Fresh Approach,Toronto, MGraw-Hill Publishing Company, 1990.

Click here to return to the Webulator Menu Page
For more information, please contact:

Professor William J. Montelpare, Ph.D.,
Margaret and Wallace McCain Chair in Human Development and Health,
Department of Applied Human Sciences, Faculty of Science,
Health Sciences Building, University of Prince Edward Island,
550 Charlottetown, PE, Canada, C1A 4P3
(o) 902 620 5186

Visiting Professor, School of Healthcare, University of Leeds,
Leeds, UK, LS2 9JT
Copyright © 2002--ongoing [University of Prince Edward Island]. All rights reserved.