Nonparametric Capability Indices

T. V. Ramanathan 1 , A. D. Dharmadhikari 2  and Bovas Abraham 3
  • 1 Department of Statistics, University of Botswana, P. B. No. 0022, Gaborone, Botswana.
  • 2 Department of Statistics, University of Pune, Ganeshkhind, Pune, India, 411 007.
  • 3 Department of Statistics and Actuarial Science, University of Waterloo, Waterloo, Ontario, Canada, N2L 3G1.


Process capability indices Cp and Cpk are widely used in statistical quality control to assess the capability of a process. These indices are defined, based on the assumption that the quality characteristic follows a normal distribution. In this paper two new capability indices are considered, which do not depend on any distributional assumptions. The estimation and asymptotic properties of the estimators of these indices are investigated. Two examples are given to illustrate the importance of the given indices and their computational procedures.

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