10. Nonparametric Methods

  1. Thomas P. Ryan

Published Online: 27 JUN 2013

DOI: 10.1002/9781118439241.ch10

Sample Size Determination and Power

Sample Size Determination and Power

How to Cite

Ryan, T. P. (2013) Nonparametric Methods, in Sample Size Determination and Power, John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9781118439241.ch10

Author Information

  1. Institute for Statistics Education, Arlington, Virginia and Northwestern University, Evanston, Illinois

Publication History

  1. Published Online: 27 JUN 2013
  2. Published Print: 26 JUL 2013

ISBN Information

Print ISBN: 9781118437605

Online ISBN: 9781118439241



  • Bayesian nonparametric decision theoretic approach;
  • Mann-Whitney Test;
  • nonparametric methods;
  • PASS;
  • sample size determination;
  • software


Nonparametric methods are frequently used with small sample sizes as large sample properties of parametric tests then do not apply. Nonparametric methods have less power than their corresponding parametric methods when the assumptions for the parametric methods are met. Although the focus in this chapter is on determining sample size when a nonparametric test is used, Walker considered a Bayesian nonparametric decision theoretic approach to sample size calculations, independent of any specific test. Okeh surveyed five biomedical journals and concluded that the Mann—Whitney two-sample test and the Wilcoxon one-sample test should be used more frequently in medical research, in which nonnormal data are widespread, with much data being ordinal. Software for sample size determination with nonparametric procedures is, unfortunately, far from plentiful. Although PASS has considerable nonparametric capability, its procedures are not menu items and consequently may be difficult to find.

Controlled Vocabulary Terms

Bayes estimator