Monday, April 13, 2015

Six sigma calculations – value added safety statistics

The concept of using error rates for safety in a six sigma methodology has interest to the continuous improvement community.  Interest yes, but functionality not so much.  The six sigma approach started in the quality statistics realm as a means to measure first pass yield where sigma is the standard deviation measurement from a normal value.  In the quality world, reducing the deviation from a standard (desired) value is a measure of quality improvement of the normal or desired value. 

·         One sigma a value of 68.5% first pass perfect quality yield

·         Two sigma – 98.5%

·         Three sigma – 99.7%

·         Four sigma – 99.97%

·         Five sigma – 99.997%

·         Six sigma – 99.9997% perfect or approximately three parts per million error rate

At the beginning of the quality revolution there was a significant effort to get to three sigma performance, or three defects out of each 1000 items produced.  As more emphasis was placed on perfection, many organizations realized how difficult it was to be perfect with all the subcomponents in an assembly especially as each error has a multiplier effect on the final product quality level. 

So what about six sigma injury levels? 

·         Our North American statistics are based on 200,000 hours, or 100 years of labor (100 people each working a year).  If this is extrapolated to a million hours (500 labor years) six sigma performance would be three total lost or decreased output hours for that amount of time.  Here the focus is on what is not desired (injuries), is totally reactive and gives no input as to what can be done to reduce injuries.  This kind of six sigma safety indicator is difficult to measure or tabulate and even if it can be done consistently, still delivers no information that can improve injury performance.

·         The focus on lagging indicators gets even more difficult as an organization’s injury rate improves (lessens).  There are fewer and fewer errors (hours of injuries) to count and the concept of diminishing returns quickly suggests changing focusing to leading indicators like safety accountabilities, which help to prevent injuries.  There are literally thousands of possibilities for leading indicator activities (those associated with upstream processes that deliver downstream results).  This kind of leading activity can be measured, reinforced and tabulated in safety dashboard indicators, which actually make a positive difference in the quest to reduce injuries.  As these leading activities become ingrained in the organization’s safety culture, new safety accountabilities can be added to refresh and renew the relentless efforts needed to eliminate injuries in the workplace.  The bottom line; move away from injury rate measurements and focus on what it takes to help reduce injury rates (safety accountabilities across the organizations personnel). 

The Doc   

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