Case Assessment and Interpretation Flashcards
What are the objectivies of the CAI model?
- improve decision making and resource allocation
- improve relationships and develop partnerships
- provide value (defined by client agency)
- service the needs of the Criminal Justice System
What does the assessment part of CAI mean?
How we manage, prioritise and triage the demand
What does the interpretation part of CAI mean?
How we report results in a logical and quantitative way
What is the first phase of the CAI model?
- customer requirment
- case information
- customer needs
What is the second phase of the CAI model?
- case pre-assessment
- determine forensic strategy
- identify propositions
What is the third and final stage of the CAI model?
- service delivery
- forensic examination
- evaluate outcomes
- interpretation and report
What are the three hierarchy of propositions?
- source (has the semen originated from the suspect?)
- activity (has the suspect had sexual intercourse with the complainant?)
- offence (did the suspect rape the complainant?)
What proposition is this: the blood on Mr C’s clothing came from Mr Z
Source (level 1)
What level of proposition is this: the glass fragments came from window X
Source (level 1)
What level of proposition is that: Mr A commited the burglary
Offence (level 3)
What level of proposition is this: Mr A was not present when the window was smashed
Activity (level 2)
What framework does the CAI model provide to the investigator?
5 points
- ensures requirements are clearly articulated
- assists in setting forensic examination strategy
- assists decision making
- provides staged information
- enhances value
What framework does the CAI model provide to the CJS?
4 points
- ensures a balanced unbaised approach
- ensures impartiality and transparency
- allows discussion of strength of evidence
- adds value
What does CAI require?
- communication between all key parties
- clear understanding of each others requirements
- agreement of forensic examination strategy
- understanding of expected outcomes
- exploration of staged apprach where possible
How do you work out the posterior odds?
likelihood ratio * prior odds
What framework does the CAI model provide to forensic scientists?
6 points
- ensures understanding of case information and issues
- leads to an agreed forensic examination strategy
- defines proposition for testing
- enables staged examination and reporting
- underpinned by sound statistical theory
- adds value to the scientists role
What is the likelihood ratio?
Probability of the evidence given the prosecution hypothesis and information divided by the probability of the evidence given the defence hypothesis and the information
What is conditional probability?
the likelihood of an event occuring given that another event has already occurred
What is independent odds?
The likelihood of two events occurring independently of each other
* the occurrence of one event does not affect the probability of the other event occurring
What was the case of Sir Roy Meadow?
He used conditional odds to work out the likelihood of another infant death when he should have used independent odds
What do the values of the likelihood ratio indicate?
1< = supports the prosecution hypothesis
1 = neutral
<1 = supports the defence hypothesis
What is the prosecutors fallacy?
When the prosecutor incorrectly interprets the probability of evidence given the defendants guilt as the probability of guilt given the evidence
What is transposing the conditional?
- Applying Bayes’ theorem
- sometimes called the prosecutors fallacy
What is Bayes’ theorem given two events G (guilty) and I(innocent)?
Pr(G|E)/Pr(I|E)= Pr(E|G)/Pr(E|I) x Pr(G)/Pr(I)
What is this an example of? If the ground is wet (B), then it is raining (A)
Transposing the conditional
it should be “If it is raining (A) then the ground is wet (B)”
The probability of the proposition, given the evidence makes this error?
Prosecutors fallacy
Using Bayes theorem, the prior odds are multiplied by what to give the posterior odds?
Likelihood ratio
Establishing the prior odds calculates?
Base rate
What is the base rate?
the prior probability of an event occurring before any new evidence is taken into account
* it represents our inital belief or expectation about the likelihood of an event based on general knowledge or historical data
What does interpretation of CAI involve?
explaining our approach to develop effective ways to present evidence and avoid misunderstanding
What is a case that shows transposing the conditional?
R v Doheny
* said that the probability that the semen came from another source is 1 in 1 billion
* it should be that the probability of a match if the semen came from another person is 1 in 1 billion
In preassessment we will need to set out the transit strategy and identify a pair of?
Propositions
What influenced forensic science as part of the Local Government Act in 1988?
Best value
Evidence that is produced to support charge/prosecution is called?
Corroborative
What did the FSS become in 1990?
Agency
What does the CJS expect of police and courts?
- intelligence - timely information to link or exclude suspects
- Corroborative evidence - to support charge/prosecution
- timely scientific support
What does the CJS expect from politicians and society?
- rapid DNA results, quality assured casework, clear statements, good testimony
- crime reduction and prevention
- partnerships in serious crime
- an objective measure of value
What is the principles of Bayes theorem?
- The probability of the evidence/findings given the proposition and the background information
- evaluation must be carried our within a framework of circumstances (info)
- scientist must make their understandings of the case circumstances clear (conditioning info)
- must consider their observations in light of the Hp and Hd
- must consider the probability of the findings if the Hp were true and the Hd were true
What was the issue in the case of Adela Rebelo?
- manner of her death
- evidence must be considered from both sides
The case of Jill Dando
- shot dead
- show importance of weight of evidence and its evaluation
- could the GSR particle be as a result of aventitious contamination
- the GSR particle was found a year after the incident - could it have stayed there that long?
What are the different strengths of support?
6 of them
- extremely strong support = 1 million
- very strong support = 10,000 - 1 million
- strong support = 1000 - 10,000
- moderately strong support = 100 - 1000
- moderate support = 10 - 100
- weak/limited support = 1 - 10
How does Bayes Theorem keep balance?
- address at least one pair of propositions, one based on the prosecution issue and one on the alternative
- if a reasonable alternative cannot be identified, the expert may address only the one proposition but making it clear they cannot evaluate the strength of the evidence
What does establishing the prior odds calculate?
Base rate
What are the key standards for an expert opinion?
Assessment part
- establishing the key issue
- identify relevant propositions
- pre-assessment
- identify potential outcomes
- assign estimated probabilities
- estimate likelihood ratios
- commissions examinations to best progress the issue in the case
What are the key standards for an expert opinion?
interpretation part
- documentation
- the key issue and propositions addressed
- examination strategies
- report and statements
- conditioning statements
- items received and examined
- significant findings and conclusions
- disclosure paragraph
What are the 7 laws and principles in forensic science?
- law of individuality
- law of progressive change
- principle of comparison
- principle of analysis
- principle of exchange
- law of probability
- law of circumstantial facts
What is the law of individuality?
- focusses on every object whether natural or man-made has a distinctive quality or characteristic which is not duplicated in any other object
What is an example of law of individuality?
human fingerprint
What is law of progressive change?
- things change with the passage of time and nothing remains consistent
- e.g. crime scenes will change due to weather, animals/humans
What is the principle of exchange?
- Locards principle of exchange
- as soon as two things come in connection with each other, they mutally interchange the traces between them
What are some examples of locards principle of exchange?
- contact between one source and another
- fingerprints
- tyre marks
- foot marks
- hair samples
- blood
What is principle of comparison?
- only likes can be compared
- requirement of providing ‘like’ samples and specimens for evaluation with the questioned item
What is principle of analysis?
- the quality of any analysis is affected by the collection a correct samples and its correct preservation
What is the law of probability?
all identifications (both inculpatory and exculpatory) are bound by the laws of probability
What is the law of circumstantial facts?
emphasizes the significance of circumstantial facts and supports that a statement given by a human may or may not be accurate
