Actuarial and clinical approaches

Traditionally, predicting dangerousness was a clinical activity which at best brought experience to bear on the process of identifying in specific individuals factors which presaged future aggression. In the 1990s the traditional studies attempting to validate the accuracy of clinicians' predictions of dangerousness have been replaced by attempts to establish actuarial approaches to risk.(28) Risk assessment has struggled to base itself on actuarial approaches which aim to apply empirically established associations between variables and the probability of future aggression. At worst, clinical approaches are the exercise of prejudice. At worst actuarial approaches amount to administering questionnaires (instruments) and assigning levels of risk to an individual based only on their particular scores.

Those sceptical of the actuarial approach argue that it is based on statistical inferences drawn from studies on populations which are difficult, or impossible, to apply to individuals. This criticism fails to understand that actuarial approaches are about assigning probabilities, not identifying the presence or absence or a property such as dangerousness. You are not entitled to say because those with schizophrenia are three to four times more likely than the general population to be assaultive (29) that an individual with schizophrenia is more violent, but you can properly say that having schizophrenia increases the probability of their acting violently. Those convicted of serious crimes of violence are reported to be three to five times more likely to have schizophrenia (!Z) which does not translate into those with schizophrenia being violent offenders but does indicate that those with convictions for violence are more likely to also have had schizophrenia. The more relevant actuarial data available, the narrower the limits to the probability prediction in the individual case. That individuals can defy the odds goes without saying but that does not vitiate the approach. The actuarial approach to predicting probabilities of violence is just a specific instance of evidence-based medicine.

There is a substantial literature on the use of actuarial methods in the prediction of the likelihood of future criminality among currently incarcerated offenders. (2 26) It is claimed that the predictors of violent recidivism are essentially the same among prisoners and psychiatric patients. (30) This assertion of sameness opens the door to the use of instruments developed for use among offender populations not only among mentally abnormal offenders but among general psychiatric patients. The instruments currently being employed for risk assessments in the mentally disordered include the Psychopathy Check List-Revised, the Violence Risk Appraisal Guide, and the Historical/Clinical/Risk-20 instrument.(2 ^l.3 and 33) The proponents of some of these actuarial instruments do not lack either confidence or enthusiasm. Hare(34) asserts that psychopathy as measured by the Psychopathy Check List-Revised is the single most important clinical construct in the criminal justice system with particularly strong implications for the assessment of risk for recidivism and violence. Furthermore, its modified form, the Psychopathy Check List-Shortened Version, is claimed to be useable with both civil and forensic populations including the mentally disordered. (35) As a bonus it is 'reliable and valid ... requires relatively little time, effort and training to administer and score'. (35> Quinsey et al.(26) write of the Violence Risk Appraisal Guide that it is a 'guarantee [of] both reliability and validity' and that it 'further weakens any remaining support for the idea that clinical intuition (or indeed any variables relying on unstructured clinical judgement) can yield usefully accurate prediction of violent recidivism'.

The derided clinical approach, though on occasion reflecting only the idiosyncratic prejudices and experience of the assessing professional, should integrate experience with knowledge drawn from the literature including actuarial evidence. In practice, Chiswick (36) argues that clinical judgement remains our best measuring device. Approaches such as functional analysis attempt to systematize clinical assessment. (3Z) To ignore the clinician's capacity to recognize patterns is almost as silly as to ignore the evidentiary base. Attempts to articulate and clarify the place of both approaches will be made below.

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