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Six Sigma


Six Sigma was designed as a set of practices to improve manufacturing processes and eliminate defects. It then started to be used more widely in other business contexts.

Six Sigma originated at Motorola in the 1970s through a focus on improving quality while decreasing production costs. In Six Sigma, a defect is defined as any process output that does not meet customer specifications.


At the core of Six Sigma is a continuous improvement cycle of five phases with the acronym DMAIC.

  1. Define
  2. Measure
  3. Analyse
  4. Improve
  5. Control



Define… the problem, the voice of the customer, and the project goals, being as specific as possible.

Measure… the key aspects of the current process and collect relevant data.

Analyse… the data to investigate and validate cause-and-effect relationships. Determine what the relationships are, and attempt to ensure that all factors have been considered. Identify the root cause of the defects being investigated.

Improve… or optimise the current process based upon data analysis using techniques and standard work flows to create a new, future state process. Run pilots to test potential improvements before implementation.

Control… the future state process to ensure that any deviations from plan are corrected before they result in defects. Implement control systems and continuously monitor the process.

Six Sigma in practice

Six Sigma is a highly-data driven approach: each step of the DMAIC cycle uses data. Therefore data needs to be of good quality with automated collection. Within the NHS, this makes it well suited to automated or semi-automated processes such as pathology, where it can be used to understand detailed pathology testing procedures including the use of analysing equipment.

Lean and Six Sigma

Lean and Six Sigma are two methodologies that can and are frequently employed together.

Lean focuses on the breadth of a process, aiming to improve end-to-end ‘flow’ and reduce waste within a process. Six Sigma focuses on achieving an in-depth understanding of parts of a process in order to reduce variance and defects.
  • Both concepts have exactly the same objective: continuous business process improvement.
  • Both follow a structured approach to identify the root causes of a business problem and find the optimal solution to avoid recurrence of the problem.
  • Six Sigma improves the capability of steps that do add value whereas Lean focuses on eliminating waste.
  • Six Sigma is a data driven methodology, whereas Lean relies more on value stream maps and subsequent analysis.

What are Lean and Six Sigma and what are the key differences between them?


Six Sigma

Speed and efficiency by identifying value add and eliminating waste
Reducing variation, improving quality and stability by using a structured DMAIC approach
Realise more with less and at low costs
  • In a Lean process there is no ‘waste’ in terms of what is not valuable to the customer.
  • Activities are error proof, and defects are prevented. Workspace lay-out is optimal and easy to understand, everything is on-hand and easy to find.
Realise lower variation in a process/product quality
  • Six Sigma is a highly disciplined, quantitative, data-driven, fact based methodology focused on developing and delivering near-perfect products and services.
  • Six Sigma is a statistical measure of how far a given process deviates from perfection.
Voice of the customer
  • Business processes are viewed ‘end to end’ from the customers’ perspective – focus on what adds value to the customer.
  • Any activity in the workflow that adds time, effort or cost but does not create value to the customer is considered as necessary non value add and/or non-value add. These are considered two types of waste.
Voice of the customer
  • Similar to Lean, Six Sigma places the customer at the centre of process improvement to ensure customer’s needs are satisfied.
  • With the voice of the customer as a starting point Six Sigma focuses first on reducing process variance and then on improving the process capability.
Improve the whole system
  • Lean focuses on the end to end process and does not typically seek to improve the activities that create existing value for the customer.
  • Instead Lean seeks to identify and reduce waste to its lowest level by eliminating non value added activities (NVA) and minimising necessary non value added activities (NNVA).
Various diagnostic techniques
  • Six Sigma projects focus on improving the root-causes of the problem, instead of improving the symptoms.
  • Diagnostic techniques: Run and Control charts, ‘As-is’ process map, Critical to Quality Tree, Pareto Chart, Flowcharts, Histogram, Cause-and-Effect Diagram, Hypothesis Testing etc.

< Step 3: Plan and implement the changes

< The Improvement Journey