upper limit of 597. The number 195 is referred to as a Lower Control Limit( LCL) and 597 is called an Upper Control Limit( UCL).( See Figure 5.)
“ What the graph tells us is that the results of all of the salespeople are between the LCL and UCL. That means that the differences in their results are attributed to factors other than the individuals’ performance,” explained Harold.
“ I just can’ t accept that, Harold,” said Jim.“ You are trying to tell me that there is no difference between a salesperson who sells $ 285,000 and a salesperson who sells $ 490,000.”
“ Not to split hairs, Jim,” said Harold,“ but that is not exactly what I said. There can be all kinds of differences between them, but what I am trying to get across is that when you take a statistical look at these nine results, the numbers do not provide any statistical evidence that any one salesperson did a better job than the others.
“ The salesperson who sold $ 490,000‘ got the sharper drills’ and the one who sold $ 285,000 got‘ material that was harder to drill,’” continued Harold.“ All kinds of factors influence sales. For instance, sometimes we have stock when your customer calls, and sometimes we don’ t. Sometimes our best customer service person answers your customer’ s call and sometimes our worst one answers. Sometimes the differences between our products and our competitors’ products work for you, sometimes they work against you. Sometimes a customer wants a product with a UL label, and sometimes the customer wants a product that carries the European equivalent of UL approval. These are things that are part of the system, and the salesperson has little or no influence over them.”
Jim could have accepted that argument if the range of numbers had not been so great.“ Are you saying if we took this set of numbers back into the factory, you would treat someone who produced 285 pieces a day the same way you would treat someone who built 490 pieces a day?”
“ Absolutely,” said Harold,“ and any factory run with statistical precision anywhere in the world would do the same thing.”
“ So,” Jim countered,“ if Deming’ s statistical systems say that anything from 285 to 490 pieces is OK and Deming is such a big deal in Japan, how come I hear so much about the consistency of Japanese manufacturing concerns?”
Harold tented his fingers in front of his face, resting the tip of his nose on his index fingers as he gave Jim’ s question some thought.“ Actually, Jim, you’ re right. A range of 285 pieces to 490 pieces is not OK. I am not saying that it is. What I am saying is that, statistically, any output between 195 and 597 is a part of the system and when the outputs are in that range they do not provide any evidence of the quality of work of any individual worker.
“ The system we are using in our example exists due to a variety of factors that are within the control of management but are outside the control of any individual worker. For example, if we always had stock, the numbers would cluster closer together. If we didn’ t run out of literature, the