In the past decade or so, the situation in clinical research has become more complex. The effects of new drugs or surgical procedures on Quantity of life is likely to be marginal indeed. Conversely, there is increased awareness of the impact of health and health care on the quality of human life. Therapeutic efforts in many disciplines of medicine—psychiatry, respirology, rheumatology, oncology—other health professions—nursing, physiotherapy, occupational therapy—are directed equally if not primarily to the improvement of quality, not quantity of life. If the efforts of these disciplines are to be placed on a sound scientific basis, methods must be devised to measure what was previously thought to be unmeasurable, and assess in a reproducible and valid fashion those subjective states which cannot be converted into the position of a needle on a dial.