Statistical Process Control
Statistical Process Control (SPC) is the process of using control charts and applying statistical techniques to monitor and control the process for compliance with specification limits. The application of SPC allows for an objective and quantitative basis of measurement, a marked improvement over the alternative method of making subjective and reactive assessments through inspection that detects and corrects problems after they occur.
Achieving process capability is not possible without understand the nature of variations in a process. Very often, the statistical tools applied remain complex, and the knowledge on how to apply such tools vague. This defeats its very purpose of using control charts and a statistical analysis.
Adopt a simple, direct, and straightforward statistical analysis to determine the extent to which the process deviates from the required parameters. Simple and straightforward tools lend clarity to the concept.
Implement measures to control the deviance from specifications, or ensure the range of control limits fall within specification limits. The way to approach the same is through a Corrective and Preventive Action (CAPA), a key element of a good manufacturing practice or (GMP), and a subsystem of the overall quality management system. This method entails a systematic investigation of the reasons for discrepancies or deviations from specifications using various analytical techniques such as a root cause analysis using the five-whys and fishbone diagrams and effecting remedial actions to resolve such root causes.
Statistical process control may unearth bottlenecks, wait times, and other sources of delays within the process that causes non-compliance with specification limits. Resolving such issues may require changes in design, and since the change involves work in process, the most viable approach is experimentation. At times experiments reveal bringing the process under statistical control requires fundamental changes such as redesigning and implementing a new process that eliminates the major sources of non-compliance.