State of Control

To maintain a state of control over testing, labs need to keep track of results over time.

One way they do this is to record results on a control chart. They use separate control charts for each type of material (tissues versus soil, for example). They call each type of material a "matrix".

Below is an example of a control chart.

Under a state of control, you would expect 1 in 20 sample results to be either above the top purple line or below the bottom purple line. You can see by the red circle that something happened to cause more results to be above the red line. This is a sign of loss of control. Other signs are groups of 5 results or more above the average or below the average, or groups of results that show a downward or upward trend.

Labs may use statistical computer programs instead of control charts. A lab should be able to show you control charts or statistical summaries.

Please continue with, "Reports".