The process is required when no other criterion is accepted as entirely adequate to define the quality to be measured. Under these circumstances a different type of evidence is required to support the supposition that a particular measure is valid. Construct validation involves assembling evidence about what a test really means - in essence we wish to know if the instrument measures what it should, does not measure what it should not, and distinguishes between groups where it should be able to. Responsiveness Responsiveness refers to the ability of a measure to detect clinically important change. It is closely related to validity, in fact, some consider it a type of validity.
Some authors use the term 'sensitivity' synonymously with responsiveness.
Conclusion Accurate outcome measurement can only be achieved if measurement instruments have been fully evaluated in terms of their scientific properties and clinical usefulness. The authors are grateful to Dr AJ Thompson for helpful discussion and encouragement in this area. A guide to rating scales and questionnaires. Feinstein A. Clinimetrics. Yale University Press 1987.