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The role of variation in product dimensions is well known to the quality profession, and the subject of process capability studies. Variation also affects, however, most business activities including services. Variation is why lines of angry customers often back up in front of service desks that have (on paper) excess capacity, and why traffic jams often appear out of nowhere. The underlying causes are similar; favorable variation does not offset unfavorable variation in these applications.

  • Recognize that variation is a form of friction, the force that, according to von Clausewitz, results in seemingly simple plans not working as expected in practice
  • Know how variation affects product dimensions (and therefore quality), and be able to explain the concept to production workers. This is the traditional application of variation
  • Recognize the role of variation in metrology, as reflected by measurement systems analysis (MSA). Know how guardbanding can reduce the risk that customers will get nonconforming work, albeit at the cost of rejecting some good work.

General Carl von Clausewitz's On War (1831) identified friction as the impediment that makes plans that seem easy on paper fail in the real world. Friction includes assignable or special cause variation, such as bad weather impeding a shipment, but random or common cause variation is yet another form of friction. It is why, in a product quality application, purportedly interchangeable parts don't interchange if there is enough variation in their product dimensions. It is also why, as shown in Goldratt's and Cox's The Goal, it is impossible to run a balanced factory at full capacity without inventory, one of the Toyota production system's Seven Wastes, overrunning the factory. Variation will similarly affect even a single workstation to the point where lines of parts or, even worse, disgruntled customers back up in front of it while it operates at below capacity. This presentation will expose the underlying root cause of these problems, and provide attendees with some off the shelf containment and corrective actions.

Attendees will also receive a target simulator that illustrates the effect of variation on product dimensions while simultaneously simulating a quincunx or Galton board, although it uses the normal distribution rather than the quincunx approach. The simulator works in Windows 7, and was scanned immediately prior to upload with two security programs.

  • Recognize how variation can affect production control (as described by Goldratt's and Cox's The Goal), and what can be done to contain the effects of the variation or even remove the variation. Recognize how this kind of variation can even affect a single workstation or service activity, in contrast to a balanced factory
  • Recognize how variation can turn a non-critical path into a critical path in project management
  • Know why frustrating traffic jams appear out of nowhere when a highway is operating at near capacity; the reason is again that favorable variation does not offset unfavorable variation

All managers, engineers, supervisors, and technicians who want to understand the effect of variation on services as well as manufacturing operations, and gain awareness of techniques to offset its effects.

William A. Levinson, P.E., is the principal of Levinson Productivity Systems, P.C. He is an ASQ Fellow, Certified Quality Engineer, Quality Auditor, Quality Manager, Reliability Engineer, and Six Sigma Black Belt. He is also the author of several books on quality, productivity, and management, of which the most recent is The Expanded and Annotated My Life and Work: Henry Ford’s Universal Code for World-Class Success.

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