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Operational Definitions(1999/02)

Lloyd Provost

Following Deming's advise, all operational definitions should contain a method of measurement or test that relates to the concept being defined. Some will contain criteria for judgment (e. g. operational definitions for classification or decision making).

For example, airlines are required to keep information on the number of late departures. The airline and the government must agree on how to measure the difference between the actual departure and the scheduled departure. Has a plane departed when the door closes, or when it is pushed back from the gate, or when it takes off?

To study and improve the process, the airline does not necessarily need a criterion to define "late", it may simply need an operational definition of the difference between scheduled departure and actual departure. For other purposes, such as reporting to the government, a criterion for judgement may also be needed. For example, the difference between departure and schedule must be compared to a criterion (2 minutes, 5 minutes, 15 minutes), to determine if the departure is late.

The following 4 examples of operational definitions in use illustrate this format:

Example 1: Operational definitions of "arrival time" and "on-time arrival" were used to compare the performance of different airlines. 

The arrival time of a flight will be the time the wheels touch down on the runway. Time will be determined by the timepiece used for navigation for the flight. An arrival will be on time if the arrival time is not more than fifteen minutes after the scheduled arrival time.

Example 2: One of the requirements in a chemical process was that the nose cone of the reactor had to be "clean" before it was installed.

The cone is clean if (1) there are no particles > 100 microns on the process side of the nose cone as viewed by a 40x microscope and (2) there is no visual fluorescence under 2700-3500 angstroms ultraviolet light.

Example 3: One of the USDA standard quality-characteristics of canned peaches is the amount of "small pieces of extraneous vegetable material".

Small pieces of extraneous vegetable material means stems less than 10 mm in length, pieces of twigs not more than 51 mm in length, and any leaf material. Other parts of the standard specify the method of measurement for length.

Example 4: In some states, the following tests are applied to determine whether a common law marriage exists:

? The man and woman have publicly declared themselves to be married.
? The man and woman have co-habitated for more than five years.
? The man and woman have co-mingled finances.

If two out of the three tests are positive, a marriage is said to exist.The initial result of developing a useful operational definition will often be to reveal the complexity of a situation that was thought to be simple.

Lloyd Provost, Associates in Process Improvement

lprovost@fc.net



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