Illustration by Rosa Bonnin

CW: Psychological disorders

What makes someone intelligent?  This question has occupied the minds of psychologists for as long as psychology has been a thing. Even longer in fact, as the first scientific writings of intelligence date back to the 16th century, some 300 years before the works of Wilhelm Wundt, William James or Sigmund Freud  – the often-named fathers of Psychology. We know that someone’s environment is important, with our upbringing and access to education going a good way towards explaining intelligence, but it isn’t the whole picture. So, are there any innate factors behind intelligence, and if so, how many might there be? Perhaps there is some biological system that makes some people good at maths, one that makes them good at writing, one that makes them particularly creative or proficient in spatial reasoning. Or perhaps not.  Statistician Charles Spearman studied the performance of schoolboys on seemingly unrelated measures of cognitive abilities, and through statistical methods that I won’t bore you with, concluded that there exists a single, underlying factor for general intelligence (here, a factor refers to an amount of variation between individuals that appears to be explained by a single cause, whether or not we know what that cause is). This came to be known as the ‘g’ factor – a factor that everyone has but that varies in magnitude, explaining different levels of intelligence. Since its publication in 1904, this idea has been debated and modified with additional lower-order factors being proposed to further explain variations in intelligence, but the idea of the g factor has stuck around and is still used to this day. Very interesting, but why is this important now? Well, something similar seems to be happening within the study of mental illness.

Within psychopathology, the study of mental illness, it is well-known that disorders rarely present themselves in isolation. Comorbidity refers to cases when an individual has more than one psychological disorder, and fellow psychology students can back me up when I say that comorbidity is the rule, not the exception. In the U.S. National Comorbidity Survey, only 26% of those who had received a diagnosis of major depression had no other psychological disorder , and a massive study of nearly six million participants carried out by Oleguer Plana-Ripoll  and colleagues in 2019 found that receiving a diagnosis of a mental health disorder increases the risk of a second diagnosis by anywhere between 2 and 48 times .

So, how might such high degrees of comorbidity be explained?  Perhaps there are a few underlying factors that cause a wide range of psychological disorders, just as with intelligence. Here is where I can finally introduce what I think is one of the most fascinating ideas in psychology:  the ‘p’ factor. Different researchers have argued for two or maybe even three factors , but work by Benjamin Lahey and colleagues in 2012 found that variation in psychopathology can  be explained best by just a single latent factor that is conceptually incredibly similar to the g factor. And so, the study of psychological disorders begins to echo the study of intelligence.

This may sound like a very bold claim, but it’s one that actually makes a great deal of sense for several reasons. For one, treatments of disorders are rarely specific to just one – antidepressants such as SSRIs  (Selective Serotonin re-uptake Inhibitors) are diagnosed for depression, obviously, but also anxiety disorders, OCD, PTSD, certain phobias , and eating disorders such as bulimia. These drugs are generally effective for all these disorders, which may seem odd at first , but actually makes a lot of sense  if we view these disorders as sharing one major factor. There’s a similar story for therapeutic treatments of disorders as well: Cognitive Behavioural Therapy, or CBT as it is more commonly known, is a widely used talking therapy wherein patients work alongside a therapist in order to change potentially harmful ways of thinking and behaving, and is generally effective for treating disorders ranging from depression, to schizophrenia, to problems related to the misuse of alcohol. If these disorders have completely different causes, such a lack of specificity within our treatments may cause us to scratch our heads. But, if we believe that there is a p factor of disorders, then suddenly the range of applications of treatments makes a lot more sense.

It doesn’t stop there though – perhaps the strongest support for the p factor comes from more recent genetic research. Modern studies tend to focus less on the role of individual genes and more on the impact of a wide range of genetic variances, as individual genes have only been found to have very small effects on our risk of psychopathology. (If you ever read a news article stating that ‘x’ gene has been identified as ‘the gene’ for a disorder, please take this with a grain of salt – it’s more than likely pop-psychology and probably explains only a minuscule aspect of what it claims to cause). I don’t want to bore you too much with the riveting world of analysing DNA, but the important bit here is that different disorders have been found to be linked to the same wide-range of genetic variances – or at least very similar ones. Is this a biological basis of the p factor? Possibly, but shared genetics definitely at least supports the idea, and quite strongly as well.

The p factor is not just a really fascinating idea though – it has some big implications for the world of psychopathology, especially in classification and diagnosis . In both the American and European diagnostic handbooks of disorders (the DSM-5 and ICD-10 respectively), disorders are considered categorical, meaning that you either have them or you do not. This is a fairly  sensible approach that aims to give psychiatrists reliable and easy-to-use diagnostic tools, but critics argue it is too mechanical, and doesn’t properly take into account the experiences and nuances of the individual. Instead, some argue that we should use a dimensional approach, which allows for varying degrees of severity of disorders. If a categorical approach is a light switch, a dimensional approach is a dimmer  – it is understood that the experiences of patients vary, and diagnosis becomes less about fulfilling a list of criteria and more about identifying those who need help. The p factor seems to support this approach, emphasising variable levels of risk among individuals.

Might this more individualistic approach catch on as a result of the p factor? It seems very plausible. The DSM-5, coincidentally published only a year after the work of Lahey and colleagues, makes a point of stating that future consideration should be given to the dimensional approach, and support for the p factor continues to grow one study at a time. When the time comes for updated versions of our diagnostic manuals, a p factor-driven dimensional approach may be a very real possibility, a prospect I personally find very exciting.

This debate is a very complex one, and one I don’t really have enough words to do justice, but the message I really want to send in this article is this: psychopathology is increasingly becoming a study of blurred lines. And that’s a good thing – by removing progressively more arbitrary divides between overlapping disorders, between having a disorder or not, we can focus more on individual experience, on identifying those who may be suffering and providing help with fewer labels and less box-ticking. The p factor is a key part of this movement, one that emphasises that the risk of disorders may be general rather than specific, and that we should give a great deal of attention to individual variation. Such a conceptualization may not just lead to a more accurate understating of mental health, but better care as well.

Psychopathology is by no means perfect, is occasionally controversial and still has a long way to go. But the p factor, following in the footsteps of intelligence, may just take it a good distance in the right direction. And that is something that I am very excited for.

If you think they may be useful, links to resources on mental health and psychological support can be found below.

Further Reading:
Benjamin Lahey and Colleagues:
Oleguer Plana-Ripoll and Colleagues:
DSM-5 Online Library:
ICD-10 Classification: