Six Sigma is about process improvement and goes far beyond product defect rates. It is an ordered, tested methodology for widescale improvement in service and manufacture. Ultimately, six sigma is not about quality improvement - it is about improving the bottom line.
There are two types of process, 'core' and 'support', and two approches, 'improvement' and 'redesign'. Core processes enjoy first priority. Note that we are talking about processes and not dpartments. Contractors may provide support processes. In the short term all processes are candidates for improvement, but periodic redesign may be called for. There are different methodologies for each.
Who are the customers of each process and what do they require / value. The Voice of the Customer must be heard through a variety of sources. Requirements may be for an output from the process or for a service as part of the process; typically both. The Kano model (categorising into basics, performance-related, or delighters) is useful.
Go to Gemba. Collect the facts, not opinions. Define the customer critical measures, not the organisation critical measures. Give preference to continuous measures rather than discrete (yes/no) measures. 'How late?', not 'If late'. Take account of variability. Use statistical tests. The measure to be used for each process should be carefully defined in terms of what to measure, where, when, and frequency of collection. Calculate the defect opportunities, and hence calculate the defect per million opportunities - Six Sigma aims at 3.5 DPMO and reduced variation. Note that variation is a big killer - far better to be consistently one day late with delivery that sometimes one week early, sometimes one week late but OK on average.
Now you can begin the DMAIC cycle: Define, Measure, Analyse, Improve, Control. There are standard steps, questions and procedures for each step depending on whether improvement or redesign is called for. An addition is Transfer - where what is achieved in one area is transferred to others. There may be an intranet for this.
A range of well-established quality and statistical methods provides support for Six Sigma. Normally there will be a Quality Council or similar steering group. A feature is strong bottom line linkage to translate improvements into money. A trained hierarchy of experts, from Green Belt to Master Black Belt undertake projects.
Note: Many other sections of this manual are relevant to six sigma, as can be seen from the diagram.