TABLE OF CONTENTS Good measures can offer invaluable information, but data which might appear as measures can also misinform or mislead. Measurement takes time, costs money, absorbs resources. To prevent wasting resources and avoid pitfalls, measurement should be purposeful, meaningful, accurate and repeatable.
The purpose of measurement is to characterize the referent, Before embarking on measurement, the referent must be clearly identified and the task defined.
The task definition should lead to the choice of characteristics to be measured. Each characteristic must be clearly understood by all concerned: each should be represented by a well established attribute, or else must be defined with the aid of well established attributes.
The accuracy of a measure depends on the instrumentation and the ability of the measurer carrying out a correct procedure. Measures should be accurate enough for the given purpose, but not more so. Weighing an object to seven decimal places of accuracy demands much more resources than weighing it to an accuracy of two decimal places. The measure must be valid in both cases, but determining weight to great accuracy would be wasted when measuring potatoes in a corner shop, whereas it may be vital in a pharmacy or analytical laboratory.
To ascertain their accuracy, measuring instruments are calibrated, regularly comparing their readings with a standard and adjusting them as necessary.
If the referent is stable (its characteristics are not unduly influenced by the measurement process and remain invariant for the duration of...
