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Why: The effectiveness equation defines the ability of a product, operating under specified conditions, to meet operational demands when called upon. This is a practical measure of how well the system is performing-not how well we want it to perform but a practical measure of how it's doing. Since all the elements are measured between 0 to 1, the elements of the equation quickly draw the eye to where opportunities exist for making improvements.

When: The effectiveness equation is useful for trade-off boxes for various alternatives when plotted on an X-Y scale for effectiveness vs net present value (NPV) for improvement alternative selections. For the elements:

  • reliability defines the probability of a failure free interval (or the complement unreliability which describes the probability of failure),
  • availability defines the probability of the system being up and alive to handle the demand (or the complement, unavailability which describes the probability of the system being down),
  • maintainability defines the probability of making repairs within the allowed repair standard,
  • capability defines the probability of production achieving the desired production results [a measure of how well the product performs compared to the standard] and frequently it is described as the product of efficiency * utilization where
  • efficiency is an output/input relationship such as (output achieved)/(the standard required)
  • utilization is how time is used such as (direct labor)/(direct labor + labor lost)

[in the old days, if this index decreased to as low as 80% we went berserk-today,
you can't get this high because of wasted time when noses are not to the grindstone!!!].

Where: It is used to describe new systems and old systems performance. Consider this example for effectiveness: If we are comparing a heavy duty truck versus a sports car for transportation, the truck may be more effective for heavy loads whereas the sports car may be more effective for acceleration and high speeds-neither are defined by the effectiveness equation until the mission is defined.

These definitions are written by H. Paul Barringer and are also posted on his web site at

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