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A True Story About Variation

A True Story About Variation

operatorTo really understand common and special causes of variation, many people must change their paradigm. The following is a true story. A plant produced several different powdered products. Each of these products was run through the same production equipment at different conditions and put into unique silos (one or more for each product type).

To ensure that the product went to the correct silo, an operator had to set up the lines from the process to the correct silo. If product was introduced into the wrong silo, that silo was cross-contaminated and the entire silo had to be sold as off- grade, at a tremendous reduction in price.

The plant leadership had a policy that anyone who cross-contaminated a silo received three days off with no pay. What type of variation did leadership assume was present? They assumed it was special cause. They assumed that the operators were at fault. One manager said that he was not going to “idiot proof” the plant.

Was plant leadership correct? The only way to find out was to collect data.

It turns out that anyone who had worked in the unit for any significant period had time off for cross-contaminating a silo. If everyone is doing it, what type of variation is it? It is common cause. And the only way to reduce common cause of variation is to change the process.

Leadership put together a team that worked on the problem. The team came up with two simple solutions: label the lines and put better lights out at night. Easy solutions but beyond the authority of the operators to get done by themselves. With the solutions implemented, the problem, which had been occurring almost every other month, went away entirely.

So simple if you understand variation. Does your leadership? Or do they blame the people all the time? Dr. Deming estimated that 94% of the problems a company faces are due to common causes; only 6% are due to special causes (that may or may not be people related). So, if you always blame problems on people, you will be wrong at least 94% of the time. It is the process most of the time that needs to be changed. Leadership must set up the system to allow the processes to be changed.

What is your story about variation?


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