Scientific value of quality of life and other subjective measurements in medical research

Quality of life measurements have invaded the world of clinicalresearch and in particular of therapeutic trials. These measurements,as the measurements of pain, fatigue, anxiety, have the peculiarityto be interested in "subjective" characteristics. An important questionarises then: to measure a subjective characteristic can it claimthe same scientific status as to measure an objective characteristic ?If the answer to this question seems a priori negative, it is reallyvery difficult, if not impossible, to find epistemological elementsallowing to differentiate the value or the quality of a subjectivemeasurement with that of an objective measurement.A point exists however. The quality of a measurement is determinedby the answer to two questions: What is the quality, reliabilityof the measurement ? What is actually measured ? In the field ofobjective measurements the answer to the second question is largelyfacilitated by the existence of solid physiopathological models.These models do not exist in the field of subjective measurements,it is thus necessary to be particularly careful, in practice, beforeaccepting that such instrument measures well what is announced inits title… This point is particularly true regarding quality of lifemeasurements.