P-Chart

Christopher Diaz OM380 November 27, 2001

P-Charts: The Proportion Defective Attribute Quality Control Charts Quality has been a concept that has been with us since the beginning of time. From the creation of the world as described in the book of Genesis in the Bible, “God pronounced his creation ‘good’—e.g., acceptable quality” (Systma). From that point on, quality has been an issue that cannot be easily defined. However, certain intrinsic elements or dimensions of quality have become more manageable and more importantly, controllable. One such element is the pchart, or a proportion defective attribute control chart. With the advent of Statistical Process Control (SPC), a new methodology process created an ongoing and continuously evolving process rather than a quick-fix quality management system. SPC uses statistics to identify quality variations in a process. Steps are then designed and implemented to correct these variations, bringing processes under ever-tighter control resulting in higher quality. With SPC, companies can monitor their processes throughout production, analyze data and take corrective action in real-time. With this monitoring, quality assurance can be determined and adhered to. There are two principal types of Quality Assurance: “sampling inspection of incoming outgoing materials (acceptance sampling) and control charts for ongoing processes (process control). Control charts differentiate between the process being in control (within an accept range of random variation) and out of control (outside the acceptable range)” (Antony 9). The primary purpose of a control chart is to detect whether a major change or shift is imminent or has occurred in a process resulting in an alteration of that process. The selection of the appropriate control chart is vital for the success of the quality of process. Attribute Control charts are used when gathered data or measurements are classified as acceptable or not acceptable (pass/fail, go/no go, good/bad)....