STATISTICAL PROCESS CONTROL CHART

A statistical process control (SPC) chart graphically displays data about some process or product. The data, based upon samples or observations, are collected over a period of time. The data, when plotted, should fall within an acceptable range, or tolerance level. Any data falling outside that range may indicate a problem or an opportunity for improvement.

A SPC chart provides several benefits. It provides for effective monitoring of processes. It also helps to identify problems when they arise. Further, it aids in capitalizing on anomalies that may, in fact, lead to better processes or products.

for Developing a Statistical Process Control Chart

• Draw an x-axis (horizontal line) to reflect a time continuum (e.g., months).
• Draw a y-axis (vertical line) for a variable (e.g., measurement criteria).
• Draw a line perpendicular to the y-axis to reflect the mean or average of the variable.
  • Note: The mean may be based on your knowledge, experience, or statistical calculation.
• Draw a dotted line perpendicular to the y-axis to reflect the upper control limit.
• Draw a dotted line perpendicular to the y-axis to reflect the lower control limit.
  • Note: Both the upper and lower control limits represent the acceptable range; anything outside the lines represents anomalies or deviations.
• Plot occurrences over a period of time.
• Identify anomalies for further analysis.