Chapter 2 The development of OASys Introduction Chapter 1 explained why it is vital to have a consistent risk needs assessment procedure to inform effective practice. This chapter explains the rationale behind the new system. It provides an overview of the research evidence which has informed the development of OASys. It describes the alternative methods of risk assessment, and their limitations. It discusses the surveys of practitioners which have been taken into account in developing OASys. Clinical versus actuarial risk assessment Traditionally there have been two main approaches to risk assessment, the clinical model and the actuarial model.
The clinical model is so called because it is diagnostic and relies on professional judgement. The most common form of clinical assessment is where a practitioner interviews the offender, consults previous records and then forms a judgement about the offender’s risk by using their own knowledge and experience to weigh the information they have collected. However, all the research evidence demonstrates this method as very unreliable. Clark et al (1993) summarise the evidence on clinical prediction of risk based on professional judgement.
Blackburn (1984) explains that there are many sources of error in clinical inference, including personal factors associated with the practitioner and the offender such as age, social class, experience and the style of the practitioner, as well as underlying beliefs and attitudes which, he suggests, create ‘illusionary correlations’ that unintentionally bias judgement. The low degree of accuracy in predicting the future behaviour of offenders using unstructured methods is by no means unique. The same problems affect mental health professionals when attempting to predict outcomes for patients, and employers using traditional recruitment and promotion interviews.
Research also shows that the degree of ‘confidence’ the professional feels about their judgement is in no way correlated with its accuracy. The evidence indicates that the main role that clinical assessment can play is in understanding the predisposing and precipitating factors associated with OASys Manual V2 © Crown Copyright 2002 Page 5