The Levey-Jennings chart is a graphical tool used in laboratory quality control to monitor the performance of a particular test or assay over time. It is named after its inventors, William A. Levey and E. Quinn Jennings.

The chart is a simple line graph with time on the x-axis and the test results on the y-axis. The mean value is usually plotted as a horizontal line in the middle of the chart, and two additional lines, known as control limits, are drawn above and below the mean to indicate the acceptable range of results.

The control limits are typically set at three standard deviations from the mean, which means that 99.7% of the results should fall within the limits if the assay is performing correctly. As new data is collected over time, the results are plotted on the chart, and any data points that fall outside the control limits are flagged as potential errors or outliers.

The Levey-Jennings chart is widely used in clinical laboratories to monitor the quality of test results and to detect any shifts or trends in the data that may indicate a problem with the assay or the testing process. It is a valuable tool for maintaining the accuracy and reliability of laboratory test results over time.