Saturday, 16 February 2013

Actuarially False

Sunday, January 27, 2013

Showdown looming over predictive accuracy of actuarials

"Large error rates thwart individual risk prediction

If you are involved in risk assessments in any way (and what psychology-law professional is not, given the current cultural landscape?), now is the time to get up to speed on a major challenge that's fast gaining recognition.

At issue is whether the margins of error around scores are so wide as to prevent reliable prediction of an individual's risk, even as risk instruments show some (albeit weak) predictive accuracy on a group level. If the problem is unsolvable, as critics maintain, then actuarial tools such as the Static-99 and VRAG should be barred from court, where they can literally make the difference between life and death."

"From both clinical and legal perspectives, it is arbitrary and therefore inappropriate to rely solely on a statistical algorithm developed a priori - and therefore developed without any reference to the facts of the case at hand - to make decisions about an individual, especially when the decision may result in deprivation of liberties. Instead, good practice requires a flexible approach, one in which professionals are aware of and rely on knowledge of the scientific literature, but also recognize that their decisions ultimately require consideration of the totality of circumstances - not just the items of a particular test."

10/07/2003. Reissued 20/04/05 

Offender Assessment and Sentence Management - OASys

"Q: How accurate is the risk predictor?

A: The risk predictor is what is known as an actuarial or statistical risk assessment tool. The risk predictor has been extensively tested and it has been found to be very reliable. Research on similar tools also suggests that they are at least as accurate as clinical judgements. It should, however, be borne in mind that a score on the scale defines the probability that an offender in general with that history of offending will be reconvicted. It does not define the probability that the specific individual offender will be reconvicted. The scale can only be an aid to judgement and one aspect of risk assessment. Other factors also have to be taken into account when assessing the risk posed by a particular offender."


Tuesday, March 5, 2013

Remarkable experiment proves pull of adversarial allegiance

"Psychologists' scoring of forensic tools depends on which side they believe has hired them.

A brilliant experiment has proven that adversarial pressures skew forensic psychologists' scoring of supposedly objective risk assessment tests, and that this "adversarial allegiance" is not due to selection bias, or preexisting differences among evaluators."


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