How does one define a mental disorder? We call them psychopathologies--diseases of the psyche. But unlike many diseases, there's no blood. No weeping sores. No physical trauma. We also refer to it as 'abnormal psychology', which begs an immediate question. What makes something 'abnormal'?
Mental health concerns are broad categories of invisible suffering. Clinicians struggle to define them. And if it's difficult for clinicians, what hope can we have for the general public?
This is no small matter. Just over half of (or as many as two in three) people will meet clinical criteria for a mental health disorder in their lifetime. About 25% within the last year. Not to mention that surveys like those linked, particularly surveys on stigmatised phenomena, tend to under-report.
Four models of mental health
Fortunately, we do have some rules of thumb we can apply. Clinicians develop their diagnoses around four models that help to narrow down the vageries of 'abnormal psychology'.
The cultural/social model
“The Cultural/Social model looks at whether the behaviour ‘breaks the rules’ of a society.”
We can start off by thinking something like 'well isn't abnormality just something that people think is weird?' It's a valid position to take. This is the 'Cultural/Social model. If certain types of behaviour break the implicit rules of a society; that is, if the stuff you're doing is seen as 'strange' or 'inappropriate', then we can use this to diagnose someone.
This is particularly useful in cases like mania. An abnormally elevated mood that can lead to some very problematic decision-making. Or schizophrenia. It's not uncommon to be annoyed at the government or the media, but it's unusual to stress about them controlling you with radio waves.
Unfortunately, there are some pretty obvious problems with this. Firstly, it's super subjective, so how does one measure it? How much weirdness is abnormal? As an example, it's pretty unusual to have 100,000 Instagram followers. But it's probably not particularly problematic.
Secondly, social norms vary wildly across time and culture. What's abnormal for me or you might not be abnormal the next country over, or fifty years ago, or more pressingly, fifty years from now. Consider homosexuality. In the 1960's this was a mental health disorder according to one extremely influential clinical manual. In the 80's it still was, but only if you were unhappy about it. And now, it's (obviously) not referenced by any of our clinical texts as an illness. What does it mean to have grown up thinking you were mentally ill, only to have that diagnoses stop existing? Can't be great.
Finally, this particular model is highly pejorative; it defines your illness by your isolation from your community.
The statistical model
“The Statistical model tries to find out what’s ‘abnormal’ by the statistical rarity of the behaviour.”
So maybe we look at something that can't be pejorative. The 'Statistical model' simply looks at behaviours that are statistically rare. Lets say only 5% of people are doing something, we might say that's sufficiently rare enough to classify as 'abnormal'. And that doesn't stigmatise either, it's just an observation of the frequency. It's easier to measure because it's objective. Much better.
That said, as mentioned before, problematic mental health isn't always so rare - half of all people is not a small proportion at all. Also, one wonders where we determine the cut off for these things. Who gets to decide that 5% of people is sufficiently rare?
More to the point, though, rarity is not always an indication of mental illness. Having a huge family is rare, but it's probably protective. Statistical abnormality is not always problematic abnormality.
The danger model
“The Danger model approaches the issue by determining whether the person is at risk of doing harm to themselves or others.”
One feature of mental illnesses that helps them stand out is that they are harmful. For example, common illnesses like depression and anxiety are risk factors for suicide. Less common illnesses like mania and psychosis can occasionally result in violence too. For these rare occasions, we can use the 'Danger model'. If you pose a risk to yourself or others, then you can be considered 'abnormal' under this rule. This has an inherent protective value. Instantly, treatment can be organised to reduce that risk of harm.
Less ideally, the danger model is prone to abuse. Since it's kind of hard to define who is at risk (how many times have you said 'I'm going to kill that person'?), it can be easily manipulated. How easily? There's a whole Wikipedia page devoted to it.
The distress model
“The Distress model simply asks the person how bad they feel it is.”
What's always worth asking, and what's missing from the other models, is a question about what the person thinks. Instead of exploring all these external facets of mental illness, we can just ask someone how they feel. This is called the 'Distress model'. Basically, if the behaviour is personally distressing or interfering significantly with the person's life, it can be seen as 'abnormal'. Since this is self-defined, it makes it very simple to measure. It's well known that different people have different tolerance to stress and different coping mechanisms. A self-definition is also less perjorative than those ascribed by danger or the cultural model. The person chooses the label.
What's less good about asking is that people don't always have insight into their problems. Again, take mania as an example. During a manic episode, one feels incredible. Problem gamblers are invested in the game. The problematic behaviours that flow from these states aren't seen as issues by the person at all. Less dramatically, we should also be careful that we don't convince ourselves that a momentary distress is a mental disorder.
Tying them together
I feel like you probably know where I'm going with this. It's impossible to just look at one facet of someone's mental health or presentation and decide whether that person is 'abnormal'. It's got to be a considered approach evaluating each of these four areas to determine what's going on. And in fact, many psychologists will simply decide that despite two or three models fitting something, it still isn't 'abnormal' enough to warrant a label. It's just a bit odd. Clinicians typically refer to two diagnostic tools, the ICD and the DSM to help formulate their decisions, but these tools are merely guidelines. They help us consider the four models and how they might apply to various clusters of symptoms. At the end of the day, a label isn't going to solve the problem. It's what you do with it that counts.