Operations / quality

Universal Measure of Quality

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 Table of Standard Quality Levels         
               
   Mean             
   Tasks       Errors       
   Between   Error   Quality   Per       
 Level   Errors   Rate   Rate      10,000  Color     
               
            4             16 6.3% 93.8%         625  Infrared     
            5             32 3.1% 96.9%         313  Red     
            6             64 1.6% 98.4%         156  Orange     
               
            7           128 0.8% 99.2%           78  Yellow     
            8           256 0.4% 99.6%           39  Green     
            9           512 0.2% 99.8%           20  Blue     
               
          10         1,024 0.10% 99.90%           10  Indigo     
          11         2,048 0.05% 99.95%             5  Violet     
          12         4,096 0.02% 99.98%             2  Ultraviolet     
               
 
             
 All quality assurance measures can use the standard scale, levels and colors 
 shown above. The levels reflect the exponential power of 2 required to achieve   
 a given mean time between errors. For example, quality level 4 reflects 1 error 
 every 16 tasks, as 16 is equal to 2 x 2 x 2 x 2, or 2 raised to the 4th power in   
 exponential notation.             
               
 Once a process measure has been defined and the process observed to be   
 “under control”, without wide swings in daily error rates or significant one time 
 events, then the average error rate can be determined.  This will set the current 
 quality level.  For example, if the observed error rate is 2.3%, then the quality   
 level is 5, as level 6 at 1.6% has not yet been attained.       
               
 Moving from one quality level to the next higher quality level requires the   
 process owner to cut the number of errors in half.  This applies to each upward 
 step.  In practice, process owners can typically move up one step every 2-4   
 months using standard root cause analysis tools.         
               
 Once the measure for a process has been defined and approved by   
 management, then the process owner reports on the monthly measured error   
 rate. A master table should be maintained showing the current quality level for 
 each defined process, and the first date at which each level was achieved.   
               
 While the ultimate goal of any process is zero defects or errors, this   
 pragmatic, incremental approach has been shown to be most effective in   
 helping front-line staff members to own and improve their processes through   
 time.               
               
 Most unmeasured processes operate at quality level 4, with a 5-7% error rate.  
 Once a process is measured, the error rate usually drops to 3-4% very quickly, 
 at quality level 5.  Once a staff member is assigned responsibility, the move to 
 quality level 6 and a 2% error rate soon follows.  These first improvements can 
 usually be done by using common sense and a little more attention. Process   
 steps are usually documented and performed consistently at this level.   
               
 Moving to level 7 and an error rate below 1% is typically much more   
 challenging.  Staff members usually need to record the details of each error   
 and analyze the errors in a time period such as a week or a month in order to   
 identify the largest cluster of problems.  At this stage, the bottleneck   
 identification and elimination techniques described in “The Goal” are very   
 useful.  Identifying the type of error, the person, the product, the time of day,   
 the machine or other sources of variability commonly leads to rapid   
 identification of the greatest problem area.  Eliminating the bottleneck can   
 often be done through manual process changes, retraining, device calibration, 
 more frequent measurements, and changes in user settings.  While computer 
 system changes may be identified at this stage, it is best to attempt to use   
 manual changes first, until these have been exhausted.     
               
 Reaching the Yellow level of stage 7 merits some celebration.  Reducing errors 
 to below one in one hundred is an important milestone.  At this point, the   
 number of errors has been cut in half 3 times for an overall reduction of 85%.    
 Fully 5 out of every 6 errors that originally occurred have been eliminated for   
 good.  Some simple processes can move straight to level 7 within a few weeks 
 or months.  It is important for staff members not to became disappointed when 
 they do more of the same good actions, but “hit the wall”, and are unable to   
 move forward as quickly, if at all, at some point.  This is normal, but there are   
 always ways to go over, around or through the wall.       
               
 The progression to Green level 8 and Blue level 9 typically requires the   
 application of more advanced quality techniques and/or the revision of   
 computer systems.  For many processes, the Kaizen approach to rapid   
 process revision can work here.  The introduction of poke yoke or failsafe   
 devices, steps, and specialized tools is appropriate here.  Moving repetitive   
 tasks to the computer is common at this time.  Staff members should have   
 been trained in quality concepts, including the basic ISO tenets of say what   
 you do, do what you say, and be able to tell the difference.  Staff members   
 should be performing all of their own measurements.  Reliance on final   
 inspection should be diminishing, as staff work quality control steps into their   
 core process.             
               
 Until a process has reached Green level 8, it is typically unwise to attempt to   
 change the underlying customer service level that is desired.  Attempting to   
 reduce a service cycle time from 14 days to 10 days when a process is not at 
 least at level 8, is likely to lead to a reversion back 2 or 3 quality levels,   
 thereby offsetting the benefit of greater speed with lower reliability.     
               
 For most processes and customers, Blue level 9, with one error for every 512   
 transactions, is at or below the threshold of materiality.  Staff members should 
 be encouraged to apply their skills to move to the next level, but be warned   
 that further improvements often require additional invest- ments in equipment,   
 computer systems or a total process re-engineering effort, including adjacent   
 processes, suppliers and customers.  Staff members should focus their   
 attention on any processes which remain at levels 4-7, before they pursue level 
 10, where errors occur once in every 1,024 transactions.  This level is usually   
 reached by front line staff with 3 or more years of quality management   
 experience or those with access to quality specialists.       

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