Nancy, what you are talking about does not just apply to psychometrics. EBM has been taking this on for years. Appendicitis is also a construct. There is no this is definitely appendicitis at this degree of inflamtion, but not at this degreee. In your example, at what value of is WBC going to considered elevated? What temp is elevated? How inflamed is the appendix? 5%? 10%? 20%? What are the PP/NP/kappa for those values?
EBM has been taking this on for years in other areas, as well. In 2013, the ACC/AHA guidelines lowered the threshold for the diagnosis of hypercholestremia and statin use. Does this mean the construct of elevated choelsterol is BS?
Finally, what about fibromyalgia? You know, the disorder that a doctor convinced was real and got other doctors to diagnose people with it?
Fair enough - but there's a spectrum of physical proof to things. Hematologists over the years have examined the blood and determined that there's a normal range for WBCs. "Inflammation" may be more nebulous but you can still look at a cell from the appendix and show that it is abnormal (for example, if it has ruptured or invaded by bacteria). You cannot do that with a brain cell that I know of, and if you can, the condition will be called "neurological" not "psychological." Psychometric testing wouldn't be needed most likely in that case.
Some people don't believe in fibromyalgia at all. I would lump it in with a lot of things in medicine that you could question whether they are real or not. What about chronic lyme disease? My point is not that non-psychiatric medical conditions are all concrete physical concepts, but rather that anything that is measured "psychometrically" relates in some way to the "psyche" and I personally know of very few, if any, physically verifiable measurements that pertain to the human psyche. (Although having a brain would be one obvious one. I would be quite confident in saying "No diagnosis on Axis I" to someone who was born without a brain. I would not doubt the validity of this non-diagnosis. But again, with such physical proof, why would I resort to psychometric testing?)
A simpler example to show my point might be a complete fracture of the femur. No one uses "psychometric testing" to evaluate femur fractures. They don't need to because a human being can see with their eyes, and with an x-ray if needed, when a femur is broken. I'm sure there are questionable cases. But you can draw a picture of a femur that is intact, and one that is broken, and most reasonable people would agree these are different physical states. I don't feel the same amount of doubt as to whether femur fractures are "valid constructs" as I do about, say fibromyalgia, or for that matter, "panic disorder with agoraphobia."
Dementia might be one case where psychometric testing can be correlated to physically measurable qualities. I'm just saying, it is part of the definition of "psychological" that things tend to be "mental constructs" as opposed to physically measurable phenomenon, and mental contracts by their very nature lead a person to not always trust that they are real.
