control limits

"Limits on a control chart which are used as criteria for signalling the need for action, or for judging whether a set of data does or does not indicate a 'state of control'" [ASQ]. Used here to refer to the defined limits or ranges of results expected due to the random error of the method, and beyond which some course of action should be taken. It is common in clinical laboratories to use Levey-Jennings control charts with limits set as either the mean plus or minus 2 standard deviations, or the mean plus or minus 3 standard deviations.