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The first time I ever heard someone say “you are normal” was as a kid when my mother peered at the thermometer she had just used to take my temperature. Apparently, the tip of the mercury had settled at the 98.6 mark on the glass device, signifying normality. The verdict meant no doctor would be making a house call to give me an injection of penicillin (which we now know would not have been appropriate even if I had fever), but also no day home from school. So much rested on being 98.6 and “normal.”
Have you ever wondered how 98.6 got to be “normal?” Numbers like that pervade clinical medicine. Laboratory tests, vital signs, and other important measures all have numerical values associated with them and most include a “normal range.” One of the most common ways that a normal range is established is to do the measurement in thousands of healthy people and see what the average result is.
In the case of body temperature, for example, a German physician named Carl Wunderlich collected armpit temperatures from over a million people and determined that normal should be established as 98.6 Fahrenheit. It turns out that he was slightly off: The average temperature for normal adults is 98.2. But even this does not tell the whole story because normal body temperature fluctuates with time of day, activity, and age and varies from person to person. So it is more correct to say that normal temperature is within a range of about 97 to 99.
How Medicine Decides What’s “Normal”
Most of these normal ranges represent what statisticians call the “normal distribution.” You have certainly seen the bell-shaped curve that describes many natural phenomena. All of the values for any given measure fall beneath the curve. The average, or mean, is represented by the line down the middle. The two lines on either side are each said to be one standard deviation from the mean. In the perfect normal distribution, 68% of the values lie within the one standard deviation lines. The two lines on either side of the one standard deviation line represent two standard deviations from the mean; 95% of the values fall within two standard deviations of the mean.
“Normal” is often said to be anything that falls within two standard deviations of the mean, or about 95% of the population. But there is one more thing that goes into determining “normal” in clinical medicine and that has to do with consequences. What difference does it make if you are outside the normal range, that is, more than two standard deviations away from the mean value of a large sample of healthy people?
Let’s take the concentration of sodium in blood, known as the serum sodium level. Every first-year medical school student knows that “normal” serum sodium for an adult is between 135 and 145. When the serum sodium level gets above 145, a condition called “hypernatremia,” a person’s cells become dehydrated and he/she will experience severe consequences that include “muscle cramps, seizures, headache, intracranial hemorrhage, lethargy, coma, and death." On the other hand, hyponatremia occurs when the sodium level is below 135, a condition that results in equally dire outcomes, including “nausea, emesis, headache, seizures, lethargy, development of focal neurologic deficits, respiratory depression, and coma." So 135 to 145 is not only a normal distribution of sodium values, it is the range that a person must be in or serious, life-threatening symptoms and physiological changes will almost invariably occur.
How simple it would be if all things in life could be boiled down to normal distributions and normal ranges, if we could know precisely—or at least within a well-defined range—what is normal and what is abnormal. Notice that in the case of serum sodium it is critically important that we agree upon what is normal and what is not. We do not say that someone with a serum sodium level of 160 is “different” or “not typical.” We say he or she has an abnormality that must be urgently addressed.
Of course, the world is not so simple and increasingly we witness disputes about what constitutes “normalcy.” Even when there are numbers available, not everyone agrees on what is normal. There is currently, for example, a dispute among leading medical associations about what is a “normal” blood pressure, with the American Heart Association and American College of Cardiology on one side of the debate and the American Academy of Family Physicians and American College of Physicians on the other side. The argument started in 2017, when the former groups issued new guidelines that lowered the definition of high blood pressure from 140/90 to 130/80. The latter two organizations refused to accept that change, saying the evidence for it is weak and that applying the new standard could cause more harm than good for patients.
This means that if you go to your doctor’s office next week and your blood pressure is 135/85, you may or may not be told you have an abnormality (in this case high blood pressure, also known as hypertension), depending on which organization your physician is listening to. The reasons for the difference of opinion among experts are complex but are essentially related to how different people look at the same data. In this case, even though we are dealing with a critical aspect of human physiological function, the pressures generated by the heart as it pumps blood through our bodies, one that can be objectively measured, “normal” is somewhat in the eye of the beholder.
The Debate Over What’s “Normal” in Psychiatry
And of course, it gets even more complicated—and sometimes divisive—when we deal with things that cannot be measured objectively with numerical results the way serum sodium and blood pressure can be. Psychologists and psychiatrists are constantly challenged to justify their “labeling” people as “abnormal.” How do we define schizophrenia, for example? First, we draw up criteria for the illness, then test whether those criteria can be reliably applied to individuals and determine if meeting those criteria has any implications for an individual’s ability to function in society. People who hear voices that aren’t there, harbor implacable fears about threats that don’t exist, and/or talk without making sense are said to have, respectively, auditory hallucinations, paranoid delusions, and thought disorder. We use structured rating scales to quantify the severity of these symptoms, but we as yet have no underlying biology that distinguishes people we say have schizophrenia from those who do not.
Science writer Jim Kozubek echoes the opinion of many critics of psychiatric diagnostic systems when he writes that “psychiatric disorders are not deviations from the norm but expressions of attributes that can be normal in their contribution to human variation and persistence in the population.” According to this view, people with schizophrenia, depression, or panic disorder are not “abnormal,” but are instead expressing human variation. They may be different, but not “sick.”
This notion was clearly energized with the publication of the American Psychiatric Association’s most recent diagnostic manual, DSM-5. With its list of new psychiatric disorders, the DSM-5 is seen by some critics as representing an attempt to justify over-treatment of people who are not really ill, especially with medications. Thus, mental health professionals are accused of pathologizing normalcy for their own professional benefit. At its most extreme, those who insist that we cannot really differentiate normal from abnormal may agree with philosopher Jonathan Sholl, who argues that “both health and disease are normal, reflecting distinct regularities and ways of living. Disease is neither unnatural nor does it signal the absence of norms: it is a matter of having different norms."
The idea that what we call “disease” really represents mere human variation might strike an oncologist or cardiologist as absurd. How can we think of a disease like glioblastoma multiforme (the most common form of brain cancer in humans) or dilated cardiomyopathy (one of the most common reasons for heart transplantation) as variations of normal? Most people do not have either condition and those who unfortunately do face very severe consequences.
Criticism of diagnostic schemes for kidney or liver disease are rarely, if ever, heard. In truth, the concern with what we call normal is most often voiced with respect to mental and behavioral disorders. Unlike brain tumors, there is nothing a pathologist can point to as being blatantly abnormal in someone with dyslexia, autism, or social anxiety disorder. Whereas social attitudes are irrelevant in determining whether a person with a significantly elevated temperature or serum sodium level will be sick or need treatment, they clearly influence how we treat people who have trouble learning how to read, do not readily make eye contact with others, or avoid social encounters because of extreme anxiety. In the absence of clear-cut etiologies and the presence of stigma, it may seem more humane to label schizophrenia and bipolar disorder as “variations” rather than illnesses.
Curiously, the debate over what is or isn’t normal rarely seems to involve people who actually have psychiatric illnesses. Does a person who experiences a panic attack every time she leaves her house object to being told she has an illness called panic disorder that usually responds to cognitive behavioral therapy? Would someone who is constantly despondent, experiences no pleasure, cannot sleep at night, and thinks being dead would be better than his present situation take solace in being told he is experiencing normal human variation? Or would he rather be diagnosed with depression and prescribed an antidepressant medication?
Making diagnoses and defining disease states is not inherently an attempt to violate the human spirit. The intention behind these activities is ideally to help us recognize situations in which people are suffering and hopefully remediate them. While it is true that not everything is as cut and dry as a serum sodium level, it hardly seems helpful to dismiss depression or panic disorder as normal human variants.
The thermometer told my mother I did not have fever as defined by a statistical construct that determines what is the normal range of human body temperature. We have no such device to help us with most behavioral disturbances, but our lack of objective measures does not mean we must engage either in creating unnecessary diagnoses on the one hand or dismissing the concept of abnormal altogether on the other. It means, instead, that we have to take extra care in labeling someone as psychologically abnormal and, when we do, ensuring that our response is as effective as possible.
