Six Sigma Principles
Six Sigma is a process improvement methodology developed at Motorola in the 1980’s to reduce defects in its processes. Its goal was to achieve a level of performance equal to a defect rate of 3.4 defects per million opportunities – this is a virtually defect free environment i.e. Six Sigma performance.
Similarly, Motorola Inc. Six Sigma methodology emerged in the 1980’s from Total Quality Management, a core element of industrial engineering. Credit for coining the term ‘Six Sigma’ goes to a Motorola engineer named Bill Smith, but the roots of Six Sigma as a measurement standard can be traced back to Carl Frederick Gauss (1777-1855) who introduced the concept of the normal curve. Six Sigma as a measurement standard in product variation can be traced back to the 1920’s when Walter Shewhart showed that three sigma from the mean is the point where a process requires correction.
Core elements of Six Sigma improvement program
Often summarised by the acronym DMAIC, there are 5 program phases:
- DEFINE the problem and what the specific Six Sigma ‘project’ is seeking to achieve. This is often where alignment with the executive/process owners occurs.
- MEASURE key aspects of current performance for the process and gather any data required to help in the next phase, including detailed process mapping.
- ANALYSE the data, doing root cause analysis to determine what is causing process variation and any associated factors. Often strongly statistical.
- IMPROVE or optimize the current process, using outputs of the analysis. This involves testing the solutions and agreeing a new process.
- CONTROL the future performance of the process to prevent defects. This is often the development of tools for management and proceduralisation.
Six Sigma critiques
The critiques of Six Sigma are summarised as (Hines et al., 2004):
- system interaction not considered – uncoordinated projects
- processes improved independently
- lack of consideration for human factors
- significant infrastructure investment required
- over detailed and complicated for some tasks
- it is the new flavour of the month
- the goal of Six Sigma (3.4 defects per million opportunities) is absolute – but this is not always an appropriate goal and does not need to be adhered to rigorously
- it is only about quality.