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P-Factor: Evidence for Existence and its Functional Role

Paper Type: Free Essay Subject: Psychology
Wordcount: 3345 words Published: 8th Feb 2020

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What is the P-factor? Discuss evidence for its existence and what is its functional role?

Psychopathology is the scientific exploration of mental disorders which attempt to fully understand the manifestations of mental disorders by investigating the genetic, biospsychsocial causes; develop classification systems (nosologies) to facilitate treatment and assist research.

Recent years have witnessed an expansion of classification research, and significant advances have been made regarding how to appropriately reconceptualise psychopathology in a data-driven way (Eaton, 2017). As a result, there has been a new interest in constructs that are transdiagnostic, such as grouping disorders based on shared symptoms with a more dimensional and functional basis for classification (Sauer-Zavala et al., 2017). Among the various transdiagnostic models that have emerged within the literature, there is one that consists of a general factor of psychopathology, also known as the p-factor, a statistical construct that saturates all mental disorders (Caspi, 2014; Kotov et al., 2017). This essay will explore this model in depth by exploring the iterations of the p-factor, its existence and its potential functional role within psychopathology.

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The psychiatric diagnostic classifications such as Diagnostic and Statistical Manual (DSM) and International Classification of Diseases (ICD) are the dominant conceptual frameworks (Carragher, Krueger, Eaton & Slade, 2015). Within these nosologies, mental disorders as distinct and dichotomous, being either present or absent (Jablensky, 2016). As research progresses, it has become apparent that classification systems do not capture the full complexity of mental disorders.

Specifically, they lack the appreciation of the extensive comorbidity, two or more disorders present at the same time or occur at different times in a person’s life) among supposedly distinct disorders and the heterogeneity within ostensibly coherent categories (Wright et al., 2013).

High rates of comorbidity are common in mental disorders. It has been stated that individuals who have one disorder are likely to meet criteria for additional disorders at rates far exceeding what would be predicted from disorder prevalence rates (Krueger & Eaton, 2015). Comorbidity has become a central point of psychopathology, to the extent that different research programmes have been developed to explain comorbidity and to revise diagnostic systems (Cuthbert, 2014: Kotov et al., 2017). Investigations of common symptoms and behaviours in children and adults have been repeatedly replicated throughout several decades and research suggests that many mental disorders are manifestations of relatively few core underlying dimensions and can be grouped together (Krueger, 1999; Markon, 2010; Lahey, 2012). 

Researchers using factor analysis as statistical technique found that disorders could be grouped into two clusters: ‘internalising’ and ‘externalising’, these findings have become a well-documented structure used within transdiagnostic research (Krueger & Markon, 2006). Internalising reflects a propensity to experience distress inwards, it accounts for comorbidity among major depression, anxiety and fear including panic, social and specific phobias. Externalising indicates a tendency to experience distress outwards, it accounts for comorbidity among substance use and behavioural problems, such as delinquent conduct and anti-social disorders (Krueger, Markon, Patrick, & Iacono, 2005). More recently, researchers have found that ‘thought disorders’ also form a coherent, third dimension which encompass psychotic disorders, and manic episodes as well as bipolar disorders (Caspi et al., 2014; Keyes, et al., 2013).

Lahey et al., (2012) examined the two domains internalising and externalising (thought disorder symptoms were excluded) and found that internalising and externalising groups were themselves correlated, suggesting that there could be one underlying factor, a general propensity to psychopathology, the p-factor. Capsi (2014) was the first to test the existence of the p-factor. A longitudinal study was conducted examining lifetime psychopathology from adolescence through adulthood (38 years old). Risk factors were measured such as personality functioning, life impairments (suicide attempts and psychiatric hospitalisation), developmental histories (family history and child maltreatment) and brain integrity (IQ and executive function). All three domains; internalising, externalising and thought were tested using confirmatory factor analysis (CFA). The results revealed a single psychopathology dimension could unite all disorder, confirming the p-factor existence. The p-factor score determines the severity of impairment and the risk of having a mental disorder. For example, a high score is associated with higher impairment, worse developmental history and more compromised function in early life (ref).

Explaining the statistical underpinnings of the p-factor is not enough to understand what it is and how it should be interpreted either at a population or individual level. Furthermore, the definition of the p-factor has been contested in a statistical and theoretical sense. One common definition that is used within p-factor research is by Caspi et al. (2018) who describes it as a single dimension that suggests that there is a common liability to all forms of psychopathology. This definition is plausible due to the correlations witnessed amongst internalising and externalising domains. However, it is not well-understood what might give rise to a general factor of psychopathology or what the common liability may be. Researchers have provided several suggestive findings and proposals in response.

One proposal by Carver and colleagues is that the core mechanism of the p-factor is poor impulse control over emotions (Carver, Johnson, Timpano, 2017). Emotion-related impulsivity includes a variety of deficits in response inhibition, such as impulsive speech and action in response to experienced emotions, cognitive impulsiveness as reflected in rumination about the cause and consequences of one’s distress, and impulsive overgeneralisation from negative events (Chamberlain, Stochl, Redden & Grant, 2018). The idea of poor impulse control as core of psychopathology disorders seems suggestive, as impulsivity is one of the most common diagnostic criteria in the DSM, especially within internalising and externalising disorders (Smith et al., 2007; Peckman & Johnson, 2018). There is substantial evidence that suggests impulsivity increases vulnerability to all psychopathology as it has been identified across a wide range of psychopathology and symptom groups (Lilenfeld, 2015;cite;cite). This is evident when evaluating poor childhood self-control and emotion dysregulation as longitudinal studies revealed that it permeates across all disorder liabilities and is a salient early development predictor of the p-factor (Synder et al., 2015).

Another proposal for the core of the p-factor is that the p-factor is a personality trait (Bender, 2018).Multiple hypotheses have been put forth to explain the ways in which personality and psychopathology are interconnected (Widiger & Smith, 2008; Oltmanns, 2018; Rosenström, 2018; Widiger, 2018). Despite the wealth of research supporting this notion, traditional nosologies have neglected to integrate personality and mental disorders, to the extent that personality disorders are presented separately from other mental disorders (cite). Regarding empirical evidence for this idea, a recent study by Oltmanns & Widiger (2018) examined three separate general factors; personality, psychopathology and personality disorders. The results demonstrated that all factors were highly correlated with one another, suggesting that what the general factors have in common is that they reflect the extent of dysfunction within the respective persons’ lives, irrespective of the cause of the dysfunction or impairment (Oltmanns & Widiger, 2018). The basis for the impairment is independent of the outcome. Sharp et al. (2015) found similar results in a wide set of personality disorders, and argued in a parallel fashion that a general factor may underlie personality pathology; in fact, Sharp et al. suggested that their general factor might be the same as the p-factor identified by Caspi et al. 2014).

A third suggestion proposed by Hankin et al., 2017 is that the mechanism of the p-factor is associated with stress. Specifically, it refers to the experience of chronic stress due to a constant exposure to challenging or threatening conditions and an inability of the person to adequately cope with the stressors. For example, if an individual experiences stressors but can cope well because of an abundance of coping resources, the p-factor score will be low as will the other domains (internalising, externalising and thought disorder). In contrast, if an individual has few coping resources, the p-factor will be high (chronic), increasing risk factors and the likelihood of experiencing severe impairments. Empirical support exists to the extent that there are strong correlations between internalising and externalising in adolescents (Conway, Hammen & Brennan, 2012). Moreover, Hankin et al. (2017) explored the association between chronic stress and psychopathology and concluded that chronic stress predicts general psychopathology.

Although all three proposals view the p-factor slightly differently, there is a common assumption that the p-factor is not defined by any single construct or mechanism but rather are related to multiple, potentially interacting, risk factors (impulsivity and stress). However, it is difficult to determine what the p-factor is and how it should be interpreted due to the infancy of this concept and the challenge it poses to the classification systems. More studies are needed to test the different proposals against each other. At this point, the definition suggested by Caspi and colleagues that the p-factor unities all disorders and influences present/absent status on hundreds of psychiatric symptoms (Caspi, 2018).

Not only have researchers struggled to agree on the definition of the p-factor, there remain doubts surrounding its actual existence. It has been suggested that the p-factor is a measurement artefact due to biased response styles for example, people may experience negativity bias or social desirability in which people systematically endorse or deny all symptoms (Lahey, Krueger, Rathouz, Waldman, & Zald, 2017; Bork, Epskamp, Rhemtulla, Borsboom & Mass, 2017). In response, researchers have found alternative ways to refute this assumption that the p-factor is solely a measurement biases.

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Lahey (2015) tested the association between parent-reported scales and teacher reports of school functioning, global impairment and academic attainment. If the p-factor was solely a response bias, it would not correlate with such external factors, i.e., teachers reports of daily functioning. The findings supported the criterion validity of the p-factor as the model which included the p-factor fit significantly better than the correlated two-factor model (only internalising and externalising).

Romer et al., 2017 took a different approach by examining neural and genetic correlates of the p-factor to confirm the meaning of a general factor for common mental health disorders. If the p-factor was only a measurement error, a meaningful neural correlate would be non-existent. The study found that neural correlates were present which suggest that the p-factor is measuring meaningful variance and mechanisms underlying a general factor amongst mental health disorders (Romer et al., 2017; cite; cite).

Several studies have examined the external validity of the p-factor by testing associations with personality (Castellanos, 2016), cognitive functions (Martel, 2017), and suicide risk (Hoertel, 2015), which all provided strong evidence that the p-factor is meaningful. The increasing amount of research that has supported the meaningfulness of the p-factor has weakened the notion that the p-factor is a measurement artefact. As well as replicating the seminal study, different variations of the p factor model has been conducted such as different samples, ages, risk factors and cultures making the p factor a robust model. However, caution should be taken when studies do not model the same in terms of symptoms as it limits how far they can be directly compared.

 The data supporting a substantive meaning of the p factor and hierarchical conceptualisation of psychopathology are abundant and clear, as epitomised in the literature mentioned within the essay. The next step is to explore the functional role of the p factor and determining whether it has a place within a clinical practice. 

As clinical practice has historically viewed mental disorders as categorical, it may be difficult to introduce a hierarchical p-factor model that is dimensional. Due to its statistical nature, there are concerns about user acceptability and usability within clinical practice. Likewise, studies demonstrating the clinical utility of the p-factor is minimal compared to the historical emphasis on discrete mental disorders (Carragher et al., 2015).

Despite the proposed challenges, p-factor studies are using more clinical samples than in previous years. One study in particular used a sample that contained individuals who were exposed to child sexual abuse, which is a risk factor diagnosis across all disorders (Hyland et al., 2018). Recent studies that used clinical samples have provided their own viewpoint on what the p-factors functional role could be within a clinical setting (Gomez, Stavropoulos, Vance & Griffiths, 2018; Hyland et al., 2018). A study by Gomez at al. (2018) examined different CFA models, including the bi-factor model (p-factor included) to test the models and the reliability of the p-factor for children and adolescence, separately. The clinical sample included clinical DSM diagnoses of the major internalising and externalising disorders, derived via clinical interviews. Results revealed that the model with the p-factor was the best fit along with supporting the p-factor within a clinical sample.

Two potential functional roles for the p-factor were stated, one functional role would be involved in prevention and intervention programmes. The initial step proposed was to incorporate all the internalising and externalising disorders to provide a comprehensive evaluation and a better understanding of a child’s or an adolescent’s psychopathology. Similar suggestions have been raised for example by Synder, Hyder and Hankin (2017) who stated a better understanding of child and adolescence over time, as level of psychopathology change with age during childhood and adolescence. This would then assist in mental health screenings for childhood and adolescence, to determine which individuals are likely to be at high risk of developing general psychopathology based on risk factors. The second functional role was that the p-factor could assist in developing a more generalised treatment, however, the study did not offer a substantive account of how such treatment might work.

Research by Meier and Meir (2017) has provided a detailed plan on how clinicians could use a generalised approach to treatment. The research has identified 14 common interventions that are common among cognitive-behavioural trans-diagnostic treatments. The proposal is a fully trans-diagnostic group treatment which is grounded in research on the p-factor. Although there are already established trans-diagnostic approaches, there have mostly focused on internalising disorders (Newby et al., 2015). Therefore, this would be moving into new territory as this treatment would need to cover all dimensions such as internalising, externalising and thought disorders. This approach makes sense if we consider the mechanics of the p factor however, it is difficult to say whether this would be successful within a practical sense.

In sum, the p-factor has the potential to provide greater clarity around comorbidity patterns, which have been a longstanding problem missed by traditional nosologies. However, there are many questions that remain unanswered with regards to the interpretation of the p-factor, and its potential functional role for practice. The realisation that mental disorders overlap and are highly comorbid needs to be accepted within the clinical practice before further advancements can happen. In addition, to all areas investigating mental disorders need to be on board to enhance better understanding and to create more comprehensive preventions and treatment.


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