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Improvement Objectives
The actual work of Quality Improvement is focussed on two equally important but different objectives. The first objective is the reduction of deviation, and the second is the reduction of variability. Both of these objectives serve to improve the reliability and consistency of processes, and so too the quality of our products and services.
Reduction of Deviation
The kinds of deviation that we want to reduce can be grouped into two categories. The first is reduction of deviation through a "zero defect rate". In this endeavour, we must aim to do the job right the first time, every time. If this means stopping the whole process when only one minor thing is wrong, than that is what you do. "Sweating the details" is the only way to do the job right. Providing the fanciest piece of pie in the world, if only half-baked, is no where near providing excellence.
The second category of deviation pertains to time. Here, we must seek to reduce deviation from an ideal "zero lead-time". Lead time is a terrific measure for quality-focussed companies, because lowering lead time is all about minimizing delays. Improvements in this endeavour translate directly into improved efficiency and effectiveness, and are never easy for your competitors to duplicate. Some examples of delays which lengthen lead times include; data-entry lag and error, incorrect specifications, excessive set-up or changeover times, defects, scrap, rework, equipment failures, undependable suppliers and subcontractors, long distances, and excessive handling.
Reduction of Variability
The second objective we must constantly pursue is the reduction of variability. To reliably and consistently produce high quality, we must decrease variability everywhere we come across it. The difference between "deviation" and "variability" is subtle but very important. If deviation reduction can be thought of as "improving the numbers", variability reduction is all about achieving greater uniformity around these improved numbers.
The inputs we use must provide consistently high quality if we are to be able to use them to consistently produce high quality ourselves. As for our processes, we must identify and eliminate the variability that is inherent in all operating systems. This may mean calibrating a machine, standardizing procedures and operating intervals, developing suppliers, leveling production schedules, establishing event protocols, implementing equipment controls or training or balancing different employees to consistently perform up to par.
Reducing the variability of our inputs, and minimizing the variability in our processes, is the way to reduce variability in our outputs. Translation - reducing variation produces more consistent, more reliable and superior quality.
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