Dear Sir, Minitab uses the target to calculate Cpm, which describes the capability of your process relative to the target and the specification limits. It may be caused by multiple and overlapping processes or by processes that generate data with well-understood, but non-normal data. The USL of $1,000 is simultaneously transformed to 6.9, producing a DPMO of 148,180. I was working on a similar project and had to combine two subsets of data for calculating process capability. To determine how our process is operating, we can calculate Cp (Process Capability), Cpk (Process Capability Index), or Pp (Preliminary Process Capability) and Ppk (Preliminary Process Capability Index), depending on the state of the process and the method of determining the standard deviation or sigma value. Figure 2 shows a process where 30 percent of the transactions proceed through a slower process than the majority of transactions. The null Hypotheses for this test is that the distribution is normal thus for data to be Normal, the P-Value must be greater than 0.05 (typically). The garage defines the specification limits. In the Figure 1 illustration above Cp > 1, which as we just learned means the car should fit in the garage. Although effective analysis of data that is not distributed normally is possible, completing one of the action steps below is beneficial for some projects to create a more useful data set: The goal of a process capability calculation is to use a sample of items or transactions from a business process to make a projection of the number of defects expected from the process in the long term. The car size represents the process limits. Excellent article. If data were stable, then may calculate capability using DPMO. If yes, the process is out of control and this must be addressed before advancing in the capability analysis. Figure 1: Calculating Process Capability with Continuous Data. Your comments below about a stable process should be highlighted more in the article. Consider CE as customer expectation. Minitab and many other common software packages report the Anderson- Darling statistic. To assure valid results when performing a capability analysis, follow these steps. Control charts for variable data requires normality so it is wise to check normality first. Different business processes may produce data with a non-normal, but well understood probability distribution. Note the difference between the observed histogram and the curve representing a normal distribution curve. This poses a problem when the process distribution is not normal. Ops, I’m sorry, I said wrong! And, of course, to find the sources of variation. One statistic is called Cnpk (for non-parametric Cpk). Process Performance denotes whether a process is performing correctly in a certain period of time within the overall requirement. Cpk tells how much clearance can be expected from the side of the car to the nearest edge of the garage. If data were stable, then calculate Cp/Cpk. We are honored to serve the largest community of process improvement professionals in the world. India - +91 9811370932, US - +1 513 657 9333, Hint: Use this calculator to compute the process capability indices (Cp, Cpk and Pp, Ppk) for continuous data having both Upper and Lower Specification Limits, Creativity and Innovation (TRIZ) Practitioner, Design Risk Analysis – Design FMEA and FTA, Sample For 1 Proportion Test (Finite Population), Sample Size Calculator For 1 Sample T Test (Finite Population), Sample Size Calculator For 2 Proportion Test (Finite Population), Sample Size Calculator For 2 Sample T Test (Finite Population), Sample size calculator for mann whitney test, Sigma Level Calculator (Discrete Data – Defectives), Sigma Level Calculator (Discrete Data – Defects), Guide to select the right Hypothesis Test, Sample Size Calculator for 1 Proportion Test, Sample Size Calculator For 2 Proportion Test, Sample Size Calculator For 1 Proportion Test (Finite Population), Sample Size calculator For 1 Sample T Test, Sample Size Calculator For 2 Sample T Test.  = estimate of the process’s standard deviation.