This paper discusses the estimation of the customary process
capability index, which is defined as the ratio of the specification
width (USL LSL) to the width of the process variability (6r). Note that we consider 6r for the width of the process variability because it is quite common in practice
to use the criterium of 3r control limits when dealing with control
charts (see Chen, 1997; Montgomery, 2009, p. 184). The
main objective of this paper is to analyze the empirical performance
of various estimators of the process capability index
and assuming different scenarios.