Once we have established a manufacturing process, we want it to remain in control, with minimum variation. This is because process variation, if it is too much, more often than not, leads to non-conformance in the product, which in practical terms means a waste of time, money, and resources for the manufacturer and potential dissatisfaction for the customer.

Trend analysis is a tool that we can use to monitor production processes, analyze process variation, identify its assignable causes and take corrective actions to bring processes into a state of control. These also meet the requirements of ISO 9000 and FDA's requirements, as well as maintain the quality of the products. This paper will explain the basic principals of trend analysis, a variety of unnatural data patterns and their probable causes.