QUALITY CONTROL 



725 



Is there any indication that the observed fluctuations in the fraction 

 defective p could have been produced by other than chance causes? 

 In other words, were apparatus Type A and apparatus Type B con- 



A M J J A 

 MONTHS 



Fig. 2a. Apparatus Type A 



J J A 

 MONTHS 



Fig 2b. Apparatus Type B. 



trolled over the given period? Furthermore, is there any indication 

 that the product could have been improved during this period without 

 changing the process of its manufacture? 



