This is from a user group message base:
Whenever people speak of Acceptable Quality Level (AQL’s) and Lot Tolerance Percent Defective (LTPD’s) and anything else regarding sampling, I am reminded of the following. This is reprinted from Roger Slater’s book “Integrated Process Management” published by McGraw Hill (I would suggest this book to anyone that is involved in quality management). Used without permission.
On August 13, 1865, Dr. Ignaz Semmelweis died…a victim of learned ignorance. Official records of the time listed the cause of death as puerperal infection; a disease Semmelweis spent most of his life fighting. But the real culprits were medical colleagues, so entrenched and contemptuous in their resistance to his methods that, after 18 years of fighting conventional wisdom and professional ridicule, Semmelweis suffered a complete mental collapse. Some say his death was suicide, brought on by a self-inflicted surgical wound, which he plunged into the abdominal cavity of a cadaver, just succumbed to childbed fever.
Dr. Semmelweis suffered the fate of those who try to change things. Although he persevered longer than most and paid a more ultimate price, Semmelweis came to know the same hostility and rejection that have come to others, before and since, who challenge prevailing wisdom and dare to show that things might be done differently and better.
In 1848-at roughly the same time as Louis Pasteur was busy establishing the validity of his “germ” theory of disease in Paris and Joseph Lister was developing antiseptic procedures in London; Semmelweis was working in Vienna on asepsis as a preventative of childbed fever. In those days, throughout Europe, of every 100 women who came to an obstetric clinic to have their babies, 25 to 30 would not leave there alive. They could be expected to contract and die of puerperal infection. Most authorities were convinced that the disease was not preventable, induced by overcrowding, poor ventilation, the onset of lactation, or “miasma.” Semmelweis not only disagreed; he was blasphemous enough to suggest that physicians themselves carried the infection.
In his earliest test of this idea, he had medical students wash their hands in a solution of chlorinated lime before examining patients. Mortality rates fell immediately in his division from 10 per 100 mothers to 1 per 100. His message was simple: if doctors would but wash their hands before examining patients, infection could be minimized and lives could be saved. Semmelweis was dismissed from the clinic a year later.
What Semmelweis overlooked in his attempt to convince others of the simple expediency of clean hands was the symbolism of the time. Physicians did not want to use a chlorine hand wash because it robbed them of an important sign of status. An accepted practice among physicians in those days was simply to wipe one’s surgical smock after treating a patient. The often-smeared surgical smock came to be a visible sign of one’s professional importance. Doctors were not about to give up so handy an index of personal worth just because some crackpot had data to show that they could save lives by washing their hands. They consciously and clearly decided to ignore-indeed, reject-factual information in order to protect and retain intact a personally cherished practice. They chose to be ignorant.
What can be learned from Semmelweis’ experience? First, we can learn that intentional ignorance can be a problem, even among the brightest of people. And, secondly, we can perhaps learn something about management for, like those 19th century physicians, many modern managers are responsible for the spread of problems in their organizations. Managers, too, practice learned ignorance.
We are faced with a paradox. We usually equate ignorance with a lack of knowledge, with too few opportunities to learn and broaden our repertoires. But, as we have seen, ignorance itself may be learned when remaining ignorant suits our personal purposes.
Why is it that people refuse to accept the obvious. It always amazes me when people use AQL and LTPD as an acceptable method (excuse?) to produce nonconforming product. By definition, AQL suggests that a certain percentage of produced product can be nonconforming, and THAT IS ACCEPTABLE! Granted, this AQL is usually agreed to between the customer and producer, but to what end. Is the consumer then producing an upper level product using an AQL from vendors to pass this level of quality to its customers. How absurd!
This is what happens when producers forget what the “P” in SPC stands for. Under the assumption that a process is operating at a capability of 4% (AQL=4.0) nonconforming, then it is accepted that 4%, on average, will be nonconforming. Would it not be more feasible to increase capability to a point where there are less than 10 PPM nonconforming and provide SPC data to verify this? Would this not decrease costs to both the producer and consumer? Would this not decrease the costs associated with sampling at all? The only sampling required would be the samples required for the SPC (or equivalent methodology) chart(s). The producer increases capability to produce more acceptable product, reducing its costs. The consumer reduces costs by reducing the number of complaints, returns, etc. Acceptance sampling is an antiquated practice that should be reviewed carefully before implementing. Do not be fooled by quick fixes and do not fall into the trap of “learned ignorance.”