Use of the control chart in clinical chemistry.

HE PRINCIPLE of the quality control chart originated with the pioneering work of Shewhart in 1931 (1) in the application of statistical methods to industrial manufacturing problems. Great impetus to the use of these methods occurred during World War II in the fields of chemical process manufacturing and munitions (2). Application of the control chart to the control of accuracy and precision of chemical analyses was a natural sequel (3, 4, 5). Levey and Jennings, in 1950 (6), were the first to suggest the use of the control chart in the clinical laboratory. The mechanics of the use of control charts and the desirability of their routine use is already firmly established. Unfortunately, however, they do no good unless used, and the author doubts that as yet they enjoy very widespread use. This is not unexpected, since there is a natural reticence in a busy laboratory to install anything that means still more work. It is the responsibility of those with experience with control charts to convince others that the small amount of added effort is actually worth while. This presentation consists of a brief review of the mechanics of those control charts most useful to the clinical chemist, followed by a discussion of their practical use illustrated by actual examples drawn from the author’s 10 years’ experience with control charts in the clinical laboratory.