The P factor of psychopathology is a proposal by psychologists Avshalom Caspi and Terrie Moffit, who suggest that psychiatric disorders have a common and not specific or differentiated (as traditionally understood) etiological basis.

Next we will see where the hypothesis of the factor P in general psychology comes from and what it proposes.

Diagnosis in psychiatry: categorical model and dimensional model

As we know them now, diagnoses in psychiatry have a recent history. This history has been particularly marked by the presence of the American model of psychiatry, whose highest representative is the American Psychiatric Association (APA).

Each year, the group of specialists assigned to the latter publishes a diagnostic and statistical manual (DSM), in which a series of manifestations known as “mental disorders” are categorized and described.

This is relatively recent (it formally began in the early 1950s) and is currently one of the most widely used criteria for understanding and dealing with such manifestations . Moreover, over time, its criteria have been modified and updated according to the needs produced within the context itself.

One of the most significant and recent changes has occurred under the need to broaden the diagnostic criteria, mainly due to the growing doubts about the specificity of each disorder. In the following paragraphs we will develop in more detail what this change has consisted of.

The categorical model

As we have seen, it was in the second half of the 20th century that the first Diagnostic and Statistical Manual of Mental Disorders of the American Psychiatric Association was published. What was initially consolidated as a compilation of research on psychopathology, soon became one of the most widely used diagnostic and clinical guidelines around the world .

At least until the first four versions of this manual, the tendency had been to define clinical entities in a specific and differentiated manner. That is, just like physical diseases, each mental disorder would have its own criteria, symptoms, course, prevalence and a particular set of characteristics . Because of this categorization exercise, it is known as a “categorical model”.

However, as time went by, it became increasingly difficult to sustain such a model with the necessary rigour: it became evident that what was defined as a specific mental disorder had much to do with one or more other disorders. This relationship between one and the other was described under the medical term of “comorbidity” , which means precisely “the presence of one or more diseases or disorders in addition to the primary one”.

Not only this, but the comorbidity turned out to be sequential, that is, over time, many diagnoses ended up triggering others. And this was repeated very often among people attending psychiatric consultations.

In addition, some studies showed that there were diagnoses with a remarkable and greater comorbidity than others . For example, personality disorders had excessively high rates (around 60% of people with a diagnosis of personality disorder had comorbidity with a diagnosis of mood).

These figures left doubts about the specificity of the classifications, in addition to the fact that they had obvious clinical consequences: many people, instead of having a single diagnosis, which allowed them to understand and modify their discomfort, obtained two or more; which could represent more harm than good.

Furthermore, the high rates of comorbidity meant that the decision on whether to treat one disorder or another (and the subsequent psychological and/or pharmacological intervention), far from falling back on empirical and objective evidence, fell on the personal criteria of the professional ; a question that was increasingly criticized by the community of specialists and those affected.

The dimensional model

The development of the categorical model indicated that it was increasingly difficult to sustain a differentiated way of defining and treating diagnoses in psychiatry. Far from being an entity with distinguishable and particular characteristics, seemed to be a wide spectrum of manifestations that could hardly be separated .

Consequently, the American Psychiatric Association itself, in its fifth version of the diagnostic and statistical manual, defends the need to create a dimensional model. This would allow diagnoses to be made by means of broad criteria which, in turn, would make it possible to understand the manifestations in a multifactorial way .

This raises an important question for specialists in psychopathology: whether, contrary to what we thought, mental disorders are not specific but have a high comorbidity index; this probably means that there is a broad phenotypic structure in their genesis.

From there, different investigations were given to the task of questioning the categorical model as well as investigating and expanding the dimensionality of the diagnosis. One of the most representative in the field of psychopathology is the proposal of the P factor .

The P factor in psychopathology: a common structure in psychiatric diagnoses?

Avshalom Caspi and Terrie Moffit, along with their collaborators, published a study in 2014 where they conducted a multifactorial analysis to evaluate a new hypothesis about the underlying structure in 10 common mental disorders among young adults (18-21 years old).

Using data from a previous multidisciplinary health study, the authors examined the structure of psychopathology considering dimensionality, persistence, co-existence and sequential comorbidity of mental disorders over 20 years.

In their research they conclude that mental disorders can be summarized from three general dimensions: internalization, externalization and thought disorders .

The first dimension is related to diagnoses of mood (such as depression or anxiety), the second is linked to diagnoses of social behavior (such as borderline or antisocial personality) and substance abuse; and the third relates to manifestations of psychosis.

The above dimensions would be supported by a general element or conditioner that contributes significantly to their structuring. This element is called “P factor” (by analogy to the concept of “g factor” in intelligence) and is originated by a genetic activity, but also by the family history of depression, anxiety, psychosis, antisocial disorders or substance abuse. In addition, the same factor may be related to potential risk elements such as a history of mistreatment or abuse during childhood.

In other words, the authors consider that the P factor, as a common structuring factor in different psychiatric diagnoses, is related to higher levels of life impairment, greater history of mental disorders in the family, higher rate of negative histories during vital development, and a higher rate of early brain function .

Thus, it is a common element in the origin, development and absence of disorders; which leads the authors to defend a “transdiagnostic” approach in psychiatry.

Bibliographic references:

  • Caspi, A., Houts, R., Belsky, D., Goldman-Mellor, Harrington, H., Israel, S. … Moffitt, T. (2014). The p Factor: One General Psychopathology Factor in the Structure of Psychiatric Disorders? Clinical Psychology Sici, 2(2): 1190-137.