A dictionary definition of quality is "a measure of excellence".I believe that when most people use the term outside of a technical sense this is about what they mean. A quality product or service is who that is really good and about which the user or consumer has little to complain. The Total Quality Movement (TQM) or " six sigma" body of thought, which was popularized by Motorola, frames quality in terms of "defect rate" and the reduction of process output variability. The six sigma quality goal is to reduce process output variability to no more than 3.4 defects per million opportunities. If you producing computer chips or pencil erasers that type of imperative makes sense.In dealing with inanimate materials, mechanical parts and a process of human design performance measured in terms of defects per makes sense and apparently the TQM movement has been successful in operations of that type. In a manufacturing process variation is undesirable and efforts to eliminate outliers and execeptions makes sense.
In medicine variation is the rule.All patients do not react the same way to a given medication and we do not know ahead of time who will benefit and who will suffer a side effect or fail to enjoy improvement.Some patient get well without treatment.Manufacturing process that turn out bad parts do not spontaneously fix themselves.A well organized and TQM manufacturing process may well achieve a 6 sigma goal of no more than 3.4 defects per million opportunities. Consider the best we may do in a highly selected group of patients with for example coronary artery disease, we may reduce the risk of a coronary event by say 22% (so far it has not been 100%). So that many patients that we treat with all of the currently recommended medications will still have a heart attack. The prestigous-and apparently rarely challenged-Institute of Medicine (IOM) had defined quality in medicine as " the degree to which health services for individuals and groups increase the likelihood of desired outcomes and are consistent with current medical knowledge". So treating the coronary artery patient with all of the currently recommended meds would be quality care as the likelihood of the desired outcome would be increased and the program is compliant with current professional knowledge. This begs the questions of what evidence is required to justify a claim of increased likelihood and who is to determine what is accepted medical knowledge.A low defect rate has nothing to do with it and the manufacturing paradigm is just not applicable.Accordingly if we wanted to measure quality in a clinic or doc's practice we could look at the treatment offered to a patient with coronary artery disease.That would be the quick and dirty way.That would be the way to do it if clinical judgment and patient values did not matter.The question arises, who will do this measurement and for what reason(s). Insurance companies and HMOs do this and their claim is they do it to improve quality and concerning that we discern another apparent definition of quality,doing things as cheaply as we can get away with it.