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Last updated: Sun, Jul 28, 2024
Pain is difficult to measure. If pain, as the IASP says, is fundamentally an "experience," then it is perfectly logical and almost necessary that it can't be measured well. We can't measure fear, love, hunger, beauty, vision, comfort, or many other fundamental human experiences. We can measure correlates of the experience and we can measure behaviors affected by the experience, but we can't measure the experience itself. Why should pain be different?
The reason that researchers are keen to find better techniques for measuring pain is of course the value that they see in such better measurements. From the researcher's point of view, the inability to measure pain well can be seen as a source of variability in experimental results that make it more difficult to come to conclusions. A researcher might look at pain observations like this:
reported pain level = real pain level +/- environmental factors +/- personal factors
Here, "environmental factors" would include anything about the environment that affects the reported pain level. It might include anything from the color and temperature of the room to who is present in it, to what time of day it is and on and on. "Personal factors" would include anything particular to the subject, from age and overall health to language skills to motivations that they might have to maximize or minimize their sense of suffering, to genetic variability, to the presence of appetizing food, and on and on.
The larger these environmental and personal factors, the more they tend to mask the "real" pain level. If the research requires that the researcher must ascertain the real pain level, this is a large practical problem for the researcher. Each of the factors that masks the real pain level should be dealt with, as a didactic acronym puts it, FiRM-ly. The factor must be Fixed (held constant), Randomized (varied randomly so that differences will average out), Modeled (observed and statistically estimated), or (in lower-case because it really doesn't solve the problem) ignored. Either of the three effective strategies takes time and attention and money.
In adversarial proceedings such as disability determination or workers' compensation adjudication, the reported pain level is for the most part legally irrelevant and the real pain level is sought. In medical diagnosis, there is often a legitimate value in knowing the real pain level, although the pain level that is perceived by the patient is also important for some purposes.
But, wait! The gate-control model and masses of related research tell us that the "real pain level" doesn't really exist. Any pain we feel passes through a complex neural network whose purpose is to adjust its level up and down from moment to moment to adapt our behavior to complex and changing biologic and social needs and opportunities. So while perceived pain is a reality, real pain level is an abstraction. It would be so useful for medical and legal purposes that it is a pity we can't measure it.
If we are looking for "real pain levels," then environmental factors and personal factors are nuisance or confounding factors. If we are looking to understand and improve the human pain experience, their importance is in their magnitude and their controllability.
The state-of-art in pain measurement is primitive. Physiological measurements have revealed some associations with pain in specific types of debilities, but haven't been established as effective either diagnostically or in treatment. Self-report measures have proven useful when group averages are important, but are a very crude tool for assessing chronic pain at an individual level. Facial expressions can be accurate though costly in cases of acute, abrupt pain, but not with the more-important chronic pain. Pain behaviors have attracted much attention, but our ability to come to conclusions about them is strictly limited by our inability to accurately measure individual pain. "Real pain level" is at best an abstraction, at worst a harmful delusion.