5. Conclusion This paper discusses the estimation of the process capability index (Cp) by using the customary estimators of the process standard deviation (r). The aim of this paper is to analyze the empirical performance of the various estimators and assuming different scenarios. For this purpose, Monte Carlo simulation studies have been carried out, and which are based upon various values of: (i) the process standard deviation; (ii) specification limits or, similarly, values of the true process capability index; (iii) sample sizes n; and (iv) number of samples m used to obtain the various estimators. We also considered different probabilistic distributions to analyze the impact of this issue on the various estimators of Cp and r. Finally, we considered off-center processes and analyzed the empirical performance of the various estimators in this situation. The empirical results are compared in terms of bias and efficiency.