Six Sigma is the most well-known quality control system. It was developed by Motorola in the 1980s to reduce errors in manufacturing to the sixth standard deviation or as close to zero defects as possible. Today, Six Sigma is not only a system of continuous evaluation, it is a suite of software products and a certification. Engineers with Six Sigma certification are trained to be expert analysts at upgrading and improving products.
One important tool for quality control is the process chart. This is essentially a check list of all of the operations needed to create a complete product. In addition, the chart is used to complete the Plan-Do-Check-Act (PDCA), a widely used quality control cycle. This cycle includes a method to observe a problem, create a possible solution, test the solution and evaluate the results. This is much like the scientific process for testing theories.
An advanced methodology of statistical process control uses software to analyze the number of defects and the probability of future ones. Standard tools include Ishikawa (cause and effect) diagrams, Pareto (bars and graphs) charts and designed experiments, which are software quality control programs. Each of these tools creates a method for statistical analysis that allows engineers to gauge whether the product is performing up to competitive standards. Experiments are done with a "control" and "out-control" group similar to the scientific method.
Software quality control takes a slightly different approach than manufacturing quality control because the product can be changed so quickly by changing a few lines of code. Software design can become so complex that errors are inevitable. Therefore, teams of engineers test individual classes of programs and then ensure that they are configured properly. Software testers look for three criteria: functionality (exterior quality), design (interior quality) and adaptability (future quality).