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 www.barringer1.com