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.