In contemporary research and clinical practice, Robert D. Hare's Psychopathy Checklist-Revised (PCL-R) is the psycho-diagnostic tool most commonly used to assess psychopathy. Because an individual's score may have important consequences for his or her future, and because the potential for harm if the test is used or administered incorrectly is considerable, the test should only be considered valid if administered by a suitably qualified and experienced clinician under controlled conditions.
The PCL-R is a clinical rating scale (rated by a psychologist or other professional) of 20 items. Each of the items in the PCL-R is scored on a three-point scale according to specific criteria through file information and a semi-structured interview. A value of 0 is assigned if the item does not apply, 1 if it applies somewhat, and 2 if it fully applies. In addition to lifestyle and criminal behavior the checklist assesses glib and superficial charm, grandiosity, need for stimulation, pathological lying, conning and manipulating, lack of remorse, callousness, poor behavioral controls, impulsivity, irresponsibility, failure to accept responsibility for one's own actions and so forth. The scores are used to predict risk for criminal re-offence and probability of rehabilitation.
The current edition of the PCL-R officially lists four factors (1.a, 1.b, 2.a, and 2.b), which summarize the 20 assessed areas via factor analysis. The previous edition of the PCL-R listed two factors. Factor 1 is labelled "selfish, callous and remorseless use of others". Factor 2 is labelled as "chronically unstable, antisocial and socially deviant lifestyle". There is a high risk of recidivism and currently small likelihood of rehabilitation for those who are labelled as having "psychopathy" on the basis of the PCL-R ratings in the manual for the test, although treatment research is ongoing.
PCL-R Factors 1a and 1b are correlated with narcissistic personality disorder and histrionic personality disorder. It is associated with extraversion and positive affect. Factor 1, the so-called core personality traits of psychopathy, may even be beneficial for the psychopath (in terms of nondeviant social functioning).
PCL-R Factor 2a and 2b are particularly strongly correlated to antisocial personality disorder and criminality and is associated with reactive anger, criminality, and impulsive violence. The target group for the PCL-R is convicted criminals. The quality of ratings may depend on how much background information is available and whether the person rated is honest and forthright.
Psychopathy, as measured on the PCL-R, is negatively correlated with all DSM-IV Axis I disorders except substance abuse disorders. Psychopathy is most strongly correlated with DSM-IV antisocial personality disorder.
Factor1: Personality "Aggressive narcissism"
Factor2: Case history "Socially deviant lifestyle".
Traits not correlated with either factor
The official stance of the American Psychiatric Association as presented in the DSM-IV-TR is that psychopathy and sociopathy are obsolete synonyms for antisocial personality disorder. The World Health Organization takes a similar stance in its ICD-10 by referring to psychopathy, sociopathy, antisocial personality, asocial personality, and amoral personality as synonyms for dissocial personality disorder.
Among laypersons and professionals, there is much confusion about the meanings and differences between psychopathy, sociopathy, antisocial personality disorder, and the ICD-10 diagnosis, dissocial personality disorder. Hare takes the stance that psychopathy as a syndrome should be considered distinct from the DSM-IV's antisocial personality disorder construct, even though ASPD and psychopathy were intended to be equivalent in the DSM-IV. However, those who created the DSM-IV felt that there was too much room for subjectivity on the part of clinicians when identifying things like remorse and guilt; therefore, the DSM-IV panel decided to stick to observable behaviour, namely socially deviant behaviours.
As a result, the diagnosis of ASPD is something that the "majority of criminals easily meet." Hare goes further to say that the percentage of incarcerated criminals that meet the requirements of ASPD is somewhere between 80 to 85 percent, whereas only about 20% of these criminals would qualify for a diagnosis of what Hare's scale considers to be a psychopath. This twenty percent, according to Hare, accounts for 50 percent of all the most serious crimes committed, including half of all serial and repeat rapists. According to FBI reports, 44 percent of all police officer murders in 1992 were committed by psychopaths.
Another study using the PCL-R to examine the relationship between antisocial behaviour and suicide found that suicide history was strongly correlated to PCL-R Factor 2 (reflecting antisocial deviance) and was not correlated to PCL-R factor 1 (reflecting affective functioning). Given that ASPD relates to Factor 2, whereas psychopathy relates to both factors, this would confirm Hervey Cleckley's assertion that psychopaths are relatively immune to suicide. People with ASPD, on the other hand, have a relatively high suicide rate.
Since psychopaths frequently cause harm through their actions, it is assumed that they are not emotionally attached to the people they harm; however, according to the PCL-R Checklist, psychopaths are also careless in the way they treat themselves. They frequently fail to alter their behavior in a way that would prevent them from enduring future discomfort.
In practice, mental health professionals rarely treat psychopathic personality disorders as they are considered untreatable and no interventions have proved to be effective. In England and Wales the diagnosis of dissocial personality disorder is grounds for detention in secure psychiatric hospitals under the Mental Health Act if they have committed serious crimes, but since such individuals are disruptive for other patients and not responsive to treatment this alternative to prison is not often used.
Because an individual's scores may have important consequences for his or her future, the potential for harm if the test is used or administered incorrectly is considerable. The test can only be considered valid if administered by a suitably qualified and experienced clinician under controlled conditions. 
Hare wants the Diagnostic and Statistical Manual of Mental Disorders to list psychopathy as a unique disorder, saying psychopathy has no precise equivalent in either the DSM-IV-TR, where it is most strongly correlated with the diagnosis of antisocial personality disorder, or the ICD-10, which has a partly similar condition called dissocial personality disorder. Both organizations view the terms as synonymous. But only a minority of what Hare and his followers would diagnose as psychopaths who are in institutions are violent offenders.
The manipulative skills of some of the others are valued for providing audacious leadership. It is argued psychopathy is adaptive in a highly competitive environment, because it gets results for both the individual and the corporations or, often small political sects they represent. However, these individuals will often cause long-term harm, both to their co-workers and the organization as a whole, due to their manipulative, deceitful, abusive, and often fraudulent behaviour.
Hare describes people he calls psychopaths as "intraspecies predators who use charm, manipulation, intimidation, sex and violence to control others and to satisfy their own selfish needs. Lacking in conscience and empathy, they take what they want and do as they please, violating social norms and expectations without guilt or remorse". "What is missing, in other words, are the very qualities that allow a human being to live in social harmony."
Early factor analysis of the PCL-R indicated it consisted of two factors. Factor 1 captures traits dealing with the interpersonal and affective deficits of psychopathy (e.g. shallow affect, superficial charm, manipulativeness, lack of empathy) whereas Factor 2 dealt with symptoms relating to antisocial behaviour (e.g. criminal versatility, impulsiveness, irresponsibility, poor behaviour controls, juvenile delinquency).
The two factors have been found by those following this theory to display different correlates. Factor 1 has been correlated with narcissistic personality disorder, low anxiety, low empathy, low stress reaction and low suicide risk but high scores on scales of achievement and well-being.
In contrast, Factor 2 was found to be related to antisocial personality disorder, social deviance, sensation seeking, low socio-economic status and high risk of suicide. The two factors are nonetheless highly correlated and there are strong indications they do result from a single underlying disorder. However, research has failed to replicate the two-factor model in female samples.
Recent statistical analysis using confirmatory factor analysis by Cooke and Michie indicated a three-factor structure, with those items from factor 2 strictly relating to antisocial behaviour (criminal versatility, juvenile delinquency, revocation of conditional release, early behavioural problems and poor behavioural controls) removed from the final model. The remaining items are divided into three factors: Arrogant and Deceitful Interpersonal Style, Deficient Affective Experience and Impulsive and Irresponsible Behavioural Style.
In the most recent edition of the PCL-R, Hare adds a fourth antisocial behaviour factor, consisting of those Factor 2 items excluded in the previous model. Again, these models are presumed to be hierarchical with a single unified psychopathy disorder underlying the distinct but correlated factors.
The Cooke & Michie hierarchical ‘three’-factor model has severe statistical problems—i.e., it actually contains ten factors and results in impossible parameters (negative variances)—as well as conceptual problems. Hare and colleagues have published detailed critiques of the Cooke & Michie model. New evidence, across a range of samples and diverse measures, now supports a four-factor model of the psychopathy construct,which represents the Interpersonal, Affective, Lifestyle, and overt Antisocial features of the personality disorder.
Psychopathy is most commonly assessed with the PCL-R,  which is a clinical rating scale with 20 items. Each of the items in the PCL-R is scored on a three-point (0, 1, 2) scale according to two factors. PCL-R Factor 2 is associated with reactive anger, anxiety, increased risk of suicide, criminality, and impulsive violence.
PCL-R Factor 1, in contrast, is associated with extraversion and positive affect. Factor 1, the so-called core personality traits of psychopathy, may even be beneficial for the psychopath (in terms of nondeviant social functioning). A psychopath will score high on both factors, whereas someone with APD will score high only on Factor 2.
Both case history and a semi-structured interview are used in the analysis.