Lean Six Sigma Statistics: Calculating Process Efficiencies in Transactional Projects

Alastair Muir is a leading Six Sigma consultant and author, and the president of Muir & Associates Consulting. He has been a Six Sigma consultant for nearly ten years for various organizations, including General Electric.

The Lean Six Sigma Statistics book contains nine chapters and three appendices. Chapter 1 briefly explains the effect of variation on the customers and shareholders and lists typical problems encountered in transactional processes such as order management and mortgage application processing. Chapter 2 covers the evolution of Lean SS and the modified DMAIC process, which includes two further steps of recognizing the need for change as the first step and sustaining the benefits of the 5‐step process.

The next seven chapters successively explain in detail each of the R‐DMAIC‐S cycle steps. Chapter 3 is very useful as it provides a flow chart of moving from mission to strategic outcomes and explains the concepts of quality function deployment, and provides an example of financial analysis of an organization to highlight strategic gaps. It is emphasized that customers expect to have services when they want and not just quickly.

Chapter 4 on Define phase not only covers the basics of SS statistics but also the types of resistance (cognitive, ideological, power driven, psychological and fear) the reasons for them, and how to deal with them. The next chapter on Measure phase describes process mapping to differentiate between value added and non‐value added activities and inter‐departmental communication. Other concepts dealt with include flow rate and cycle time, process yield and efficiency, failure mode and effect analysis, and different types of data, and probability distributions.

Chapter 6 focuses on analyzing the data collected during the measure phase. It is shown that the variance to customer want (VTW) does not follow any well‐known distribution and tools for examining such sets to identify the prime factors that cause customer dissatisfaction are explained with the help of examples from patients' arrivals in a walk‐in medical clinic and call centre service times. The need for analyzing and tabulating information for different customer segments, service offering, etc. is clearly explained.

The use of improvement techniques based on lean manufacturing concepts is covered in the next chapter. The final two chapters on Control and Sustain phases are rather comparatively short. The chapter on control includes the topic of risk management. The chapter on sustain covers assessment and certification of Black Belts and the relative competencies of different roles from executive to Green Belts over the R‐DMAIC‐S phases.

Appendix A demonstrates the application of Monte Carlo simulation, using Crystal Ball, a Microsoft Excel add‐on, to identify the key steps effecting cycle time for an insurance underwriting process and a medical claims process. Appendix B provides an example of the application of Process simulation utilizing ProcessModel5 software (www.promodel.com). Appendix C is a brief (four pages) introduction to MINITAB statistical package.