Control Charting and Process Capability Statements: Issues and Resolution
Abstract: For a given process, do you think everyone would create a similar looking control chart and make a comparable statement relative to its control and capability? Not necessarily. Process statements are not only a function of procedural characteristics and sampling chance differences but can also be very dependent upon sampling approach. The implication of this is that one person could describe a process as being out of control, which would lead to activities that immediately address process perturbations as abnormalities, while another person could describe the process as being in control. For this second interpretation, the perturbations are perceived as fluctuations typically expected within the process, where any long-lasting improvement effort involves looking at the whole process. During this session, issues with traditional control charting techniques (e.g., x-bar and R charts) and process capability indices statements (e.g., Cp, Cpk, Pp, and Ppk) will be discussed. An enhanced alternative predictive performance measurement system will then be described that not only provides resolution to these issues but can also provide a predictive statement, which everyone can understand.
Keywords: Control charts - Statistical process control - Process capability - Scorecards - Dashboards