Quality Control

In our chapter on the normal distribution we illustrated the important idea of the probability distribution of the sample mean with an example of a process control chart. While the probability distribution of the sample mean based on a known population standard deviation was known since the time of Gauss, the application to manufacturing control, as suggested in the example, did not take place until the third decade of the twentieth century. It appears to have been an outgrowth of the emphasis on small samples and exact sampling distribution theory begun by Gosset in 1908 and extended greatly by R. A. Fisher by the early 1920s. [1]