Definition
Charts of individual observations in chronological order.
In detail
A trend chart is a graph that plots individual observations over time to show how data changes. It helps teams quickly identify process stability, seasonal patterns, or abnormal fluctuations and is a foundational tool for problem-solving and process monitoring. Unlike control charts, trend charts have no control limits, making them more suitable for initial exploration rather than strict statistical judgment. Typical output is a line chart with a time axis and data points, serving as a starting point for further analysis (e.g., control charts).
Example in practice
The customer service center records daily customer complaint counts and plots a trend chart. Through observation, it is found that complaints rise significantly on Mondays and decline on weekends. The team investigates further and finds that Monday accumulates order issues from the weekend. They adjust scheduling and processes, adding staff on Mondays. The trend chart is continuously tracked, confirming the improvement is effective, and complaints level off.