Data analysis is a fundamental requirement in the Six Sigma methodology for identifying process inefficiencies and reducing defects.
Basic six sigma statistics is the foundation for six sigma projects. Numerically describe the data that characterizes process Xs & Ys.
Process Performance (Pp, Ppk) helps determine if your new process is acceptable by measuring ratios of distribution to spread and centering.
Cp and Cpk are considered short-term potential process capability measures for a process. We want to describe this quality in terms of sigma.
You use non-parametric hypothesis tests when you don’t know, can’t assume, and can’t identify what kind of distribution your have.