Welcome back to the third installment of our Book Club
Part 3: Assessing Performance
Continuing our read of the book: Lean Six Sigma for Dummies by John Morgan and Martin-Brenig Jones, we are now continuing onto Part 3 of the book which consists of Chapters 6 to 8.
Chapter 6 – Gathering Information
One key Lean Six Sigma principal is “Managing by Fact” – which emphasizes the importance of capturing accurate and good data. The importance of having the right data will assist in developing the appropriate solutions to issues right down to the root causes. It can be difficult to decide what and what not to measure as Lean Six Sigma requires “Managing by Fact” and having more data doesn’t necessarily mean having the right data.
A Data Collection Plan can be developed with 5 steps.
- Figuring out key Critical to Quality (CTQ) – satisfying outputs
- Establish operational definitions to help the entirety of the team understand the who, what, where, when, and how of what is being measured
- Establish rules to ensure data is valid and consistent – ensure that data is repeatable and reproducible via gauge R&R process across both continuous and attribute data
- Data Collection itself
- Figuring out methods to improve the data collection process
The book walks us through each step of the process in detail and provides diagrams and methods to ensure the reader understands how to undergo each step to successfully gather data.
Chapter 7 – Presenting Your Data
This chapter keys in on variation, and how to understand and identify it via use of statistical process control (SPC) and control charts. There are two types of variation:
- Natural (Expected) Variation
- Special Cause (Unexpected) Variation
Chapter 7 makes key note to look at data in both numerical and visual form to better visualize variations.
Control charts are used to identify and understand variation. They are calculated using results from the processes and represent the actual data – the control limits shown are representative of the process in and of itself without any bias or tampering. Also note, that even if a process is within control limits, that does not necessarily mean that the results are good.
To assess the performance of a process, two capability indices are introduced which compare process performance and variation to CTQ’s: CP Process Capability – a simple and straight forward indicator of process capability, and CPK Process Capability Index – the adjustment of CP for the effect of a non-centered distribution. For the process to be in control, CPK < CP. The book further illustrates and describes how these indices can be used to determine the quality of our process and whether it is in control within specification limits.
In addition to control charts, hypothesis tests are utilized at a specific sample point in time to determine if the differences are statistically significant or not, typically at a 95% confidence level. Two hypothesis tests that can be used are the T-test, and ANOVA.
Chapter 8 – Analyzing What’s Affecting Performance
In this chapter several methods are depicted to assist us find the root causes of issues that degrade the overall performance of our processes.
One such method is generating a cause & effect or fishbone diagram which organizes and groups ideas, where the main “bones” of the fish are major issues, and smaller bones protruding from there are potential causes.
To ensure that managing is done by fact in Lean Six Sigma, other tools that were explored earlier in the book such as the interrelationship diagram which helps confirm the issues that were identified in fishbone diagram, and SIPOC Diagrams to see the overall flow of the process. From there we can graph out variables between X – the leading indicators and Y – the lagging indicators to determine if there are clear cause and effect indicators are in place. A scatter diagram can be used to identify correlations or relationships exist between X and Y, this is explored in-depth with provided examples in this chapter.
The final concept explored in this chapter is Takt time, which the longest acceptable time required to meet customer demand. Takt time is tied into the relationship of cycle time and activity time, where ideally takt time should be equal to cycle time.
We would love to engage those of us following along to explore this book (and others in the future!). We welcome your thoughts and feedback along the way as we grow into our Lean Six Sigma journey and the embrace of continuous improvement and increased productivity.
For more in-depth knowledge, and hands on training, you and/or your organization should consider one of GO Productivity’s Lean Six Sigma. We help provide you skills and coaching on your projects, and how to be more productive and improve your bottom line!
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