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Chapter 10

PSYC39H3 Chapter Notes - Chapter 10: Mental Health Professional, Base Rate, Risk Assessment

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David Nussbaum

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Chapter 10: Risk Assessment
What is Risk Assessment?
- In the past, risk was a dichotomy either dangerous or not dangerous
- Now, risk is a range can vary in degree to which you are dangerous
- Risk assessment includes a prediction and management component
o Prediction probability that you will commit future criminal acts, focus is to identify
risk factors
o Management development of interventions to manage/reduce likelihood of future
violence, identify what treatments might reduce level of risk
Risk Assessments: When are They Conducted?
Civil Setting
- Civil commitment individual is to be hospitalized voluntarily if mentally ill and poses a
danger to self or others; mental health professional needs to know about probability of
- Child protection protect from abuse, need to know about risk factors predicting childhood
- Immigration laws need to know about risk before letting them into Canada
- School and labour regulations include provisions to prevent endangering others
- Duty to warn mental health professionals need to tell others if their patients may act in
violent manner and need to intervene to prevent this behaviour
Criminal Setting
- Pretrial, sentencing, release can be denied bail; if higher risk, send to secure custody
- Lawyer must be able to talk about risk levels with client and when there is clear, serious
danger, public safety outweighs solicitor-client privilege
- Risk assessment is a core component of legislation determining what a “long-term offender”
should be defined as
Types of Prediction Outcomes
- 4 possible outcomes
o True positive correct prediction, occurs when a person who is predicted to be
violent engages in violence
o True negative correct prediction, occurs when a person who is predicted not to be
violent doesn’t act violently
o False positive incorrect prediction, occurs when person is predicted to be violent
but isn’t
o False negative incorrect prediction, occurs when person is predicted to be
nonviolent but acts violently
The Base Rate Problem
- Base rate represents the % of people within a given pop who commit a criminal act
- Hard to make accurate predictions when base rates are too high or too low e.g. base rates
for school shootings are low because they occur infrequently, when predicting you would
say that too many people are wrongly being predicted as potential shooters
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A History of Risk Assessment
- In the past, they didn’t care about how well risk was assessed but then they wanted to see
how accurate mental health professionals were in predicting violence
- Baxstrom study detained beyond his sentence expiry, was then released, and a lot of
other people were released as well
- Dixon study led to 400 patients being released into the community
- In both studies, base rate for violence was low and false positive rate was too high people
said that this testimony should be barred from courtroom
- Both Canadian and US courts still allow these predictions as they don’t violate any
fundamental justice rules
Methodological Issues
- Measuring risk is hard because the best way to do it is to release high-risk people into the
community and then evaluate them
- 3 main weaknesses of research on prediction of violence
o Limited number of risk factors being studied violence is a complex behaviour so
there are many risk factors involved but we only study a few of them
o Criterion variable (variable you’re trying to measure) – some use official criminal
records but many crimes are not reported, need to combine multiple methods
o How the criterion variable is defined
Judgment Error and Biases
- People use heuristics to make decisions and these can lead to inaccurate decisions
- Illusory correlation belief that correlation exists between 2 events that in reality are either
not correlated or correlated to a much lesser degree; e.g. thinking there is high correlation
between mental illness diagnosis and risk level
- Tendency to ignore base rates of violence or rely on highly salient/unique cues, e.g. bizarre
- People are usually overconfident in their judgments but they might not be accurate
overconfidence bias
Approaches to the Assessment of Risk
- Unstructured clinical judgment decisions characterized by a substantial amount of
professional discretion and lack of guidelines; no predefined rules about what risk factors
should be considered, what sources of info should be used, or how risk factors should be
combined to make a risk decision; factors vary depending on clinician
- Actuarial prediction decisions are based on risk factors that are selected and combined
based on their empirical or statistical association with a specific outcome; factors are the
same for each clinician; mechanical prediction
- Structured professional judgment decisions are guided by a predetermined list of risk
factors that have been selected from research and professional literature; judgment of risk
level is based on evaluator’s professional judgment
- Violence-risk-assessment approaches have 4 components
o Identifying empirically valid risk factors
o Determining a method for measuring these risk factors
o Establishing procedure for combining scores on risk factors
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