Psychopathy is a personality disorder defined by a constellation of affective and behavioral symptoms. The symptoms of psychopathy include shallow affect; lack of empathy, guilt and remorse; irresponsibility; impulsivity; and poor planning and decision-making (Kiehl & Hoffman, 2011). The best current estimate suggests that just less than 1% of all non-institutionalized adults meet criteria for the disorder (Hare, 1996). The base rate of psychopathy is higher in institutional settings, with an estimated 15-25% of incarcerated individuals meeting criteria for the disorder.
It was Philippe Pinel (1745-1826) (Figure 1), the founding father of modern psychiatry, who first described a group of patients afflicted with mania sans délire (insanity without delirium)(Pinel, 1801). The term was used to describe individuals who had no intellectual problems but a profound deficit in behavior typified by marked cruelty, antisocial acts, alcohol and drug use, irresponsibility, and immorality. Pinel described a type of “moral insanity” that occurred in the absence of confusion in mind and intellect, differentiating these cases from patients with psychotic behaviors.
Importantly, psychosis and psychopathy are not the same. Psychosis is a loss of contact with reality that leads to symptoms like hallucinations, delusions, and disordered thoughts. Psychosis presents itself in disorders like schizophrenia, bipolar disorder, and major depression. Psychotic symptoms are not typically observed in individuals with psychopathy. Indeed, it was the absence of psychotic symptoms that originally differentiated individuals with psychopathy from other patient groups.
German psychiatrist, J.L.A. Koch (1841-1908) (Figure 2), coined the term psychopastiche, or psychopath, in 1888. Koch claimed that psychopathy arose from a flaw in one’s constitution at birth. Constitutional psychopathy became a popular disorder in the literature of the early 1900s.
Koch recognized that assessing psychopathic traits requires a holistic appraisal of the patient’s life history. This gestalt view is necessary to accurately characterize psychopathic traits in an individual. Koch’s strategy is generalizable to assessing all personality traits and was included in the 8th edition of Emil Kraepelin’s classic textbook on clinical psychiatry (Feuchtersleben, 1845).
Even though Koch’s psychopastiche construct was more focused than the concept “moral insanity,” it was still sufficiently broad to encompass personality disorders generally. Psychopastiche constituted people who hurt themselves (i.e., suicide attempts) as well as others. This overly encompassing definition lost sight of the moral disability that is central to what is today known as psychopathy.
By the 1920s psychiatry was using the word psychopath to include people who were depressed, weak-willed, and excessively shy and insecure—in other words, it became a placeholder for abnormal psychology.
Psychopathy vs. Sociopathy
In 1909, Birnbaum suggested that sociopathic might be a better term than psychopathic to describe individuals with this particular constellation of symptoms. Birnbaum believed that antisocial behavior rarely stemmed from constitutional flaws in character. Rather, he felt that most antisocial acts emanate from the operation of societal forces that make the more acceptable forms of behavior difficult to learn (Birnbaum, 1909). One of the immediate problems with the diagnosis of sociopathy was that it, like many of its predecessors, was too broad and encompassed far too many individuals. Literally every criminal met the criteria for sociopathy as it was defined. Unfortunately, the term sociopathy has been used in colloquial settings interchangeably with psychopathy ever since.Psychopathy and sociopathy generally refer to the same set of symptoms, but sociopathy connotes social origins, whereas psychopathy is agnostic to etiology, meaning social and biological reasons are equally plausible. The term sociopathy is not used in modern academic circles anymore.
A closely related construct to psychopathy, is anti-social personality disorder (APD). APD is defined in the DSM-V as a having a pervasive disregard for and willingness to violate the rights of others (DSM-V, 2013). While most individuals with APD d0 not meet the diagnostic criteria for psychopathy, psychopaths are almost invariably diagnosed with APD (Harpur,1994). APD is more closely correlated with Factor 2 of the PCL-R than Factor 1. It is also important to note that unlike APD, psychopathy is actually not in the DSM, but is still a very useful clinical diagnosis in a forensic context.
Modern Conception of Psychopathy
In 1941, Dr. Hervey Cleckley published the first edition of The Mask of Sanity (Figure 3), a compilation of clinical research and case studies conducted with a wide variety of psychopaths from both community and institutional settings. The title refers to the “mask” of normalcy psychopaths put forth, hiding what Cleckley describes as a serious, yet unappreciated psychiatric defect (Cleckley, 1976). After nearly fifty years of clinical work and through four subsequent editions of The Mask of Sanity, Cleckley’s characterization of psychopathy is still used today. His work is considered to be of seminal importance and The Mask of Sanity remains one of the most influential clinical descriptions of the disorder.
Measurement Tools and Assessment of Psychopathy
The two most common ways to assess psychopathic traits are to use expert rater devices and self-report inventories.
Hare Psychopath Checklist-Revised (PCL-R)4) created the Psychopathy Checklist (PCL) in 1980 and revised it in 1991 (PCL-R) (Hare, 1991) (Figure 5). The Psychopathy Checklist and its successors remain the most widely used expert-rater devices to assess psychopathy today (Craig et.al, 2008). The PCL-R comprises twenty items that are used to assess the presence of psychopathic traits in adults. The standard procedure to complete the PCL-R is comprised of two parts. The first part includes an extensive review of collateral sources of information (e.g., reports about family, education, extra-curricular activities, work history, relationships with family and friends). The second part of the assessment is a detailed life history interview with the patient. The in-person interview is strongly recommended but not required to validly complete the Psychopathy Checklist provided there is sufficient collateral information on the patient. Thus, the Psychopathy Checklist can be completed even if the patient refuses to cooperate in the interview. Using all available information, the expert rates the patient on the 20 items according to very specific scoring criteria articulated in the PCL-R manual. The scores on the PCL-R range from 0 to 40. The average PCL-R score in the general male population is 4 out of 40. The mean PCL-R score in male prison samples is 22. A score of 30 or higher is considered a high score. Thirty is one-standard deviation above the mean score of prison samples and is the score typically used to signify high, or diagnostic, levels of the traits. Approximately 15-25% of incarcerated males will meet criteria for psychopathy, using 30 as the cut-off score.
Psychopathic traits are less common in females than in males. However, within forensic samples, females show a similar distribution of psychopathic traits as men. The mean Psychopathy Checklist score for female offenders is 19 with a standard deviation of 7.5 (Hare, 2001).In addition to the PCL-R, Dr. Hare and collaborators also developed the PCL- SV (screening version) and PCL-YV (youth version)(Figure 6). The PCL-SV is a shorter version of the PCL-R and is useful for assessing psychopathy in non-forensic populations. The PCL-YV is a twenty-item test specifically designed for the assessment of psychopathic traits in males and females between 12 and 18 years old (Neumann et. al., 2006). However, the label psychopathy is not advisable in minor populations. Rather these latter traits are referred to as callous/unemotional traits in youth.
There is now a well-developed peer-reviewed literature on the use of expert-rated devices to assess psychopathy. The PCL-R has been translated into over 16 languages and is used around the world in forensic settings to assess the disorder.
Diagnostic and Statistical Manual for Mental Disorders (DSM) conception of psychopathy
The DSM is the standard guidebook for defining mental illnesses in the United States. It provides a template for how clinicians assess and classify patients into various categories of mental illness. Determining a patient’s diagnosis is usually the first step towards determining the best course of treatment. However, defining mental illness is a complicated process and the DSM is an evolving document.
While almost everyone recognized the importance of the affective traits Cleckley articulated as central to the construct of psychopathy, some psychiatrists had doubts about the average clinician’s abilities to reliably detect affective criteria (e.g. lack of empathy, guilt or remorse). It was this tension—between those who did and did not think the affective traits could be reliably diagnosed—that drove the swinging pendulum of the American Psychiatric Association’s Diagnostic and Statistical Manual for Mental Illnesses (DSM) classification of psychopathy over successive iterations (Kiehl & Hoffman, 2011).
There was widespread dissatisfaction (Hare, 1998; Livesley & Schroeder, 1991; Widiger & Corbitt, 1995; Widiger et al., 1996) with early versions of the DSM’s treatment of Antisocial Personality Disorder/Psychopathy. This led the American Psychiatric Association to conduct field studies in an effort to improve the coverage of the traditional symptoms of psychopathy. The result was that the DSM-IV reintroduced some of the affective criteria the DSM-III left out, but in a compromise it provided virtually no guidance about how to integrate these symptoms. This has led to substantial confusion within the clinical community.
The DSM conceptualization of Antisocial Personality Disorder is very broad and approximately 80% of prison inmates will meet criteria for the disorder. Thus, the condition has very little predictive utility within forensic samples because it is essentially synonymous with criminality. And in the opinion of the authors, criminal behavior, per se, is not a disorder.
Confusion between the DSM concept of Antisocial Personality Disorder and the Hare Psychopathy Checklist (PCL-R) assessment of psychopathy remains problematic in many academic and forensic circles. The two expert-rater devices are very different, and their labels should not be used interchangeably. The DSM Antisocial Personality Disorder construct is not a sufficient proxy for a PCL-R score.
Thus, given the limitations of Antisocial Personality Disorder as defined by the DSM, the most common expert-rater instrument to comprehensively assess psychopathic traits remains the Hare Psychopathy Checklist-Revised (PCL-R).
Whereas clinicians typically use expert-rater instruments to assess psychopathy in forensic contexts, researchers have developed a number of self-report inventories to assess psychopathic traits in non-institutionalized populations (e.g., undergraduate students). Self-report scales are typically quicker to collect than expert-rater instruments and they require little clinical training to administer and score.
Some notable self-report psychopathy scales include:
- Self-report Psychopathy Scale (SRP) (Hare, 1985)
- Levenson Self Report Psychopathy Scale (LSRP)(Levenson et. al., 1995)
- Psychopathic Personality Inventory (PPI)(Lilienfeld & Andrews, 1996)
- Parent and teacher reports for assessment of callous/unemotional traits in youth (Frick et. al., 2003)
- Lynam’s Self-Report Child Psychopathy Scale (Lynam, 1998)
- Minnesota Multiphasic Personality Inventory (Lilienfeld, 1999)
- Gough Socialization Scale (Taylor et. al., 2000)
Self-report measures of psychopathy have been shown to modestly correlate with expert-rater devices (Kedrick & Funder, 1988). However, there are several limitations of self-reports that are worth mentioning.
First, self-report scales require cooperation. Many individuals may be unwilling to complete the scales if they are to be used in an adversarial legal proceeding, such as a risk assessment. As noted above, expert-rater instruments can often be completed even if the client refuses to participate in the process. Also, a central characteristic of psychopathy is lying and conning behavior. Self-report scales are more likely to be susceptible to manipulation than expert-rater devices.
Second, self-report scales typically require an eighth grade or higher reading level and vocabulary. Such abilities are often lower than normal in forensic populations. Also, to the extent an individual with psychopathy lacks insight into his psychological state, he will not be able to accurately assess his own behavior and its impact on other people (Miller et. al., 2011). It may be inherently problematic to ask a psychopath to report on the presence or absence of emotions such as guilt or fear if they have never experienced them (Cleckley, 1941/1988).
Third, self-report scales may also be more susceptible to the current mental state of the participant. For example, if the client is currently depressed they may endorse self-report items differently than if they are not depressed. Psychopathic traits are stable, enduring traits that are present in multiple domains of a person’s life. Thus, any procedure to assess the traits needs to be immune from acute psychological states (e.g. anger, depression, etc).
Self-report assessments of psychopathy generally remain limited to academic inquiries. Due to the limitations articulated above, they are not widely recommended for use in clinical samples, especially in forensic and adversarial settings. Nevertheless, self-report instruments are widely used in research and have led to numerous insights regarding the condition. For these reasons, the author’s recommendation is to collect both expert-rater data and self-report inventories of psychopathic traits whenever possible.
Symptom Profiles, Factors and Facets of Psychopathic Traits
Statistical techniques have been used to parse psychopathic traits into two underlying dimensions or factors. Each dimension may also be meaningfully expressed as comprising one or more facets (Hare & Neumann, 2006). Factor 1 (composed of facets 1 and 2) measure interpersonal (e.g. glibness, grandiosity, pathological lying, conning behavior etc.) and affective (e.g. lack of remorse or guilt, shallow affect, lack of empathy, failure to accept responsibility etc.) traits. Factor 2 (composed of facets 3 and 4) measure lifestyle (e.g. need for stimulation, parasitic lifestyle, lack of realistic long term goals or plans, impulsivity, irresponsibility etc.) and antisocial/developmental (e.g. early behavioral problems, juvenile delinquency, poor behavioral controls, revocation of conditional release, criminal versatility etc.) tendencies (Hare & Neumann, 2009).
It is important to note that psychometric analysis of the different factors and facets of psychopathy is an active area of academic research. A number of different models have been proposed and meaningful relationships have been found between the different factors, facets, and external variables. For example, Factor 1 seems to be positively correlated with intelligence scores whereas Factor 2 appears to be negatively correlated with intelligence scores (Blonigen et al., 2010).
Forensic Utility of the Construct of Psychopathy
The PCL-R was designed to assess psychopathic traits in the clinical tradition articulated by Cleckley. However, many studies have shown that the PCL-R scores predict recidivism, which has contributed to its widespread use in the criminal justice system.
A meta-analysis examining the relationship between PCL-R scores and violent recidivism among both sexes and juvenile and adult populations yielded a mean weighted Cohen’s d of .47 across 68 effect sizes (Leistico, Salekin, Decoster, & Rogers, 2008; Rice & Harris, 2005). Additional meta-analyses yielded a mean (weighted) AUC of .67 across seven effect sizes, (Walters, 2003) and .66 across 24 effect sizes (Campbell et. al., 2009). These results amount to moderate effect sizes in the behavioral sciences (Cohen, 1988). Additionally, two meta-analyses of PCL-Youth Version scores and violent recidivism yielded AUC’s of .64 across twenty (Oliver et. al., 2009) and fifteen (Edens et.al., 2007) effect sizes, also indicating moderate predictive value. The PCL-R has also demonstrated significant predictive value with respect to sexual recidivism, particularly when combined with a measure of sexual deviance (Hawes et. al., 2012).
The PCL-R is also used as a component of several instruments that were explicitly designed to assess future risk of violence. The following are popular risk assessors that incorporate the PCL-R:
- Violence Risk Assessment Guide (Quinsey et. al., 1998)
- Historical-Clinical-Risk Management 20 (Webster et. al., 1997)
- Domestic Violence Risk Assessment Guide (Hilton et. al., 2008)
It is important to note that the PCL-R may not predict recidivism in all populations. For example, there is little research examining the Psychopathy Checklist’s ability to predict recidivism in adolescent females and non-Caucasian adult male populations (Edens, Magyar & Cox, 2013).
Due to the significance of the PCL-R in forensic settings, including determination of liberty and death sentences, careful scrutiny of its predictive value is essential. Indeed, judges and parole boards often use the PCL-R to predict future dangerousness, equating high scores with higher risk of recidivism (Freedman, 2001). Accordingly, misuse of the PCL-R in incarcerated individuals could have serious consequences (Edens, 2001). Thus, it is strongly advised that specifically trained experts administer and score the PCL-R in appropriate contexts (Hare, 2003).
Causes and Precursors
The causes and specific pathophysiology of psychopathy are an active area of research. Like other mental illnesses, psychopathy appears in all races and cultures. Cleckley and other authors have long noted that psychopathy may manifest in both genders, in all socio-economic strata, and in all cultures and races (Cleckley, 1941/1988). At the present time, the general consensus is that a genetic predisposition is necessary for psychopathy while environmental conditions determine its specific expression (Porter, 1996).
Taxon versus Dimensional Constructs of Psychopathy
One preliminary question regarding the etiology of psychopathy is whether the disorder is dimensional or categorical in nature. As with most personality disorders, this is an ongoing topic of research in psychopathy. Several types of statistical analyses have been performed to examine the latent structure of psychopathy using PCL-R scores, including factor analysis (Blackburn & Jeremy W. Coid, 1998) and model based cluster analysis (Hicks, et. al., 2004). However, dimensional and categorical assumptions are built into factor and cluster analyses, respectively. These tests do not determine whether a construct is categorical or dimensional (Walters et. al., 2007). On the other hand, taxometric analyses were specifically designed to identify discrete versus dimensional structures. Taxometric studies of the PCL and related instruments have yielded mixed results, (Walters et. al., 2007) rendering the latent structure of psychopathy yet undetermined.
Further controversy over the latent structure of psychopathy relates to a more general problem in personality disorder diagnosis; namely, the cut off for pathological behavior is inherently normative. In other words, it is an oxymoron to suggest that someone is a “successful” psychopath because by definition, to be afflicted with a personality disorder (e.g. psychopathy) one must have pathological symptoms that cause impairment in multiple domains of one’s life.
Nevertheless, individuals who evince elevated psychopathic traits, but not at pathological levels, may appear to a layperson to have psychopathy but in actuality they do not likely have clinical levels of (all) of the traits.
Preliminary research indicates that there are correlations between physical neglect, absentee father, whether either parent was incarcerated, low socioeconomic status, young mother, depressed mother, and general instability in the family with psychopathic traits in adults (Patrick, 2005). Another study looking at adult male psychopathic and nonpsychopathic criminals showed that aversive familial and societal experiences in childhood were both correlated with adult male psychopathy (Marshall & Cooke, 1999). These conditions are hardly dispositive of psychopathy however and likely only produce psychopathic outcomes when a certain genotype is present.
A more nuanced look at the relationship between psychopathy and environmental conditions revealed correlations between childhood abuse and the irresponsible lifestyle and impulsivity facet of psychopathy (Pothyress, 2006). Again, the prevailing pathogenic hypothesis of psychopathy is a diathesis stress model similar to that of schizophrenia; i.e. a certain genotype must be present which interacts with aversive environmental conditions in order for psychopathy to manifest (Porter, 1996).
It should also be noted that many clinicians have noted that individuals with psychopathy often are raised in average to above average home environments (Cleckley, 1941/1988). Thus, the precise environmental risk factors for psychopathy remain elusive.
Genetic studies using the twin method (Plomin, DeFries & McClearn, 2008) have shown moderately strong genetic and non-shared environmental precursors of adult psychopathy (Waldman & Rhee, 2006). For example, a study using the Psychopathic Personality Inventory (PPI) self-report scale showed genetic effects accounting for 29% to 56% of variance within dimensions of psychopathy, while shared environmental factors did not account for any PPI facets (Blonigen et. al., 2003). Another study looked at callous-unemotional traits and antisocial behavior in seven-year-old twins (Viding et. al., 2005). The conclusions of this study suggest callous-unemotional traits are strongly determined by genetic influences, while antisocial behavior in the absence of callous-unemotional traits has strong shared and non-shared environmental influences. Further research is necessary to determine the generalizability of these findings to non-twin children, as well as examining the predictability of different callous-unemotional traits and antisocial behavior presentations in children on the development of clinical levels of psychopathy as an adult.
An additional line of genetic research in psychopathy focuses on a variant of the monoamine oxidase A (MAO-A) gene and its correlation with psychopathic traits (Frazzetto et. al., 2007). The gene variant identified produces less MAO-A enzymes (Young et. al., 2006). Low MAO-A phenotypes coupled with adverse childhood experiences have been shown to correlate with low thresholds for violence and aggression (Caspi et. al., 2002). While there is no gene for antisocial behavior or psychopathy, MAO-A may be a useful predictor of relevant neurophysiological vulnerabilities that when certain environmental conditions are present (e.g. abuse or neglect in childhood), an antisocial or psychopathic personality emerges.
Primary vs. Secondary Psychopathy
Psychopathy may emerge from a number of different pathways. One conceptualization suggests two dichotomous origins, termed primary and secondary psychopathy (Karpman, 1941). In this model, primary psychopaths arise from largely genetic factors whereas environmental factors play a stronger role in secondary psychopathy. Secondary psychopaths are believed to have high levels of anxiety while primary psychopaths are low anxious individuals (Newman et. al., 2005).
There is substantial evidence that anxiety can play a mediating role in a many psychopathologies, including psychopathy. However, there is insufficient evidence supporting the etiological processes thought to underlie primary versus secondary psychopathy at this time.
Neuropsychological Profiles of Psychopaths
The general finding is that there is no relationship between classic neuropsychological tests and clinical levels of psychopathy (Hart et. al., 1990).
A significant body of research regarding emotional processing abnormalities in psychopaths continues to emerge. Research suggests that deficits in emotionally relevant decision making is largely constitutive of psychopathy (Koenigs & Newman, 2013). Decision making itself, however, is a complex and multifaceted cognitive function. Substantial research is dedicated to identifying the specific information- processing skills relevant to decision making that are disrupted in psychopathy. For example, one influential hypothesis suggests that an inability to generate fearful responses underlies psychopathy (Lykken, 1957). Other research points to abnormalities in the deployment of attention that go beyond affective processing (Hiatt, 2004). Another line of inquiry suggests a general deficit in the perception, reasoning, and management of emotional states in oneself and others among psychopaths using a well-validated test of emotional intelligence (Ermer et. al., 2012).
The last decade has seen a significant increase in brain imaging studies of psychopathy. Current research support the hypothesis that psychopathic traits are associated with abnormalities in the amygdala; orbital frontal cortex (OFC); and extended paralimbic structures, prominently the temporal pole (superior temporal gyrus) and anterior and posterior cingulate cortex (Kiehl et. al., 2001). Moreover, patients with lesions in the anatomical areas relevant to psychopathy present with psychopathic-like symptoms further suggesting that temporolimbic network dysfunction is integral to this disorder (Boccardi, 2013).
Another prominent model of psychopathy hypothesizes that psychopaths suffer from associative learning dysfunction associated with selective amygdala and OFC abnormalities. Associative learning is believed to be crucial to healthy socialization (Blair, 2003).
While the etiology of these brain abnormalities are unknown, clinical data suggests that the affective dysfunction associated with these paralimbic structures are present at a young age (Frick, 1998). Moreover, longitudinal studies have found high year-to-year stability of psychopathic traits in at risk males ages 8 to 16 (Obradovic et. al., 2007). This further supports the hypothesis that psychopathy is a developmental condition with strong genetic loading.
Psychopathy and Crime
The best current estimate is that just less than 1% of all noninstitutionalized males aged 18 and over have psychopathy (Hare, 1996). This translates to approximately 1,150,000 adult males who would meet the criteria for psychopathy in the United States today (U.S. Census Bureau, 2010). And of the approximately 6,720,000 adult males that are in prison, jail, on parole or probation, 16%, or 1,075,000, are psychopaths. Thus, approximately 93% of adult male psychopaths in the United States are either in prison or jail or on probation or parole.
Psychopathy is a significant predictor of general recidivism (Hart et al., 1988), violent recidivism (Rice & Harris, 1997), and sexual violent recidivism (Rice & Harris, 1995). Simply put, individuals with psychopathy, who represent approximately 15-25% of the prison population, recidivate at higher rates, and more quickly, than the other 75-85%. The average inmate with psychopathy is back and forth to prison three times before the average non-psychopath with the same sentence makes it back once (Rice & Harris, 1995). The average incarcerated adult with psychopathy has been convicted of committing four violent offenses before age 40 (Hare et al., 1988).
Co-Morbidity with Substance Abuse
Psychopaths are at a markedly higher risk for developing substance abuse problems than the general population (Smith & Newman, 1990). Substance abuse is highly correlated with Factor 2 symptoms, which are associated with poor behavioral controls, and weakly correlated with Factor 1 symptoms, which relate to affective dysfunction (Smith & Newman, 1990).
Female psychopathy research is significantly more limited than work done in male populations. This is in part due to the relatively lower prevalence rate of females with psychopathy. In a 1997 study, researchers found that the rate of psychopathy in female prisoners was 15.5% (Salekin et. al., 1997). Moreover, research examining the correlation between PCL scores and recidivism generated different results between male and female populations. The overall predictive value of PCL-R scores on recidivism in female offenders remains uncertain (Salekin et. al., 1995).
One promising approach to treatment for psychopathy has been targeting youth who are on a high-risk trajectory towards developing the condition as adults. In a longitudinal study measuring the effects of the Mendota Juvenile Treatment Center (MJTC) on antisocial behavior in high-risk juvenile offenders, treatment emphasizing interpersonal relationships and social skill acquisition was correlated with marked decrease in criminal recidivism, particularly violent recidivism, compared to high-risk youth who did not receive this treatment (Caldwell et al., 2012). The MJTC program provided intensive, year long, cognitive behavioral therapy and produced a significant reduction in violent outcomes. It is not clear whether the program “cured” psychopathy, but it at least altered the most salient and destructive manifestation of psychopathy—propensity for aggression (Caldwell, 2013).
There has been little research in the way of treatment for adults with psychopathy. Indeed, there has never been a single published randomized treatment control study for psychopathy. Unfortunately, there remains a pervasive perception in the clinical community that adult psychopaths are impervious to treatment (D’Silva et. al., 2004). A meta-analysis of research on treatment outcomes in psychopathy concluded that the vast majority of the studies conducted lacked proper experimental design and scientific validity (Caldwell, 2013). Accordingly, it is premature to make any conclusions regarding the treatability of adult psychopathy. Clearly more treatment studies are needed.
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