CAI Flashcards
what 3 things does the criminal justice system expect of forensic science from the police and courts?
1 - intelligence - timely information to link or exclude suspect (DNA, fingerprints, mobile phones, CCTV)
2 - corroborative evidence - to support charge/prosecution
3 - timely scientific support through all stages of CJS
what 4 things does the criminal justice system expect of forensic science from politicians and society
1 - rapid DNA results, quality assured casework, clear statements, good testimony
2 - an impact on crime, crime reduction & crime prevention
3 - partnership projects in serious & volume crime
4 - an objective measure of ‘value’
what 2 things happened in 1990 surrounding the origination of CAI
1 - forensic science services (FSS) became an Executive Agency of Home Office
2 - direct charging of police for forensic services
- development of ‘forensic products’
- costs no longer ‘invisible’ to police
what 5 things was the FSS doing in 1999
1 - experiencing significant case backlogs & long turnaround times
2 - constantly re-negotiating delivery dates
3 - drowning in unnecessary examinations & lengthy (manual) analytical processes
4 - struggling even to meet some court dates
5 - failing to meet the needs of police & CJS clients
what were 2 typical submission requests in 1999
- “… forensicate (sic) these items”
- “.. I need a ‘full forensic on these items”
what did the 1988 local government act of finance statue cause
1 - ‘best value’ requirement - local government review of services
2 - police authorities were not exempt
3 - forensic costs no longer invisible
4 - cost review = better resource allocation = best value
what is best value not equal to?
best value ≠cheapest option
what are the 4 objectives of the CAI model
1 - improve decision making and resource allocation
2 - improve relationships and develop partnerships
3 - provide value (defined by client agency)
4 - service the needs of the criminal justice system
what are the 2 elements of CAI
- assessment
- interpretation
define the assessment element of CAI
how do we manage, prioritise and triage the demand
define the interpretation element of CAI
how do we report results in a logical, quantitative way
what are the 3 phases of the CAI model
1 - customer requirement, case information, customer needs
2 - case pre-assessment, determine forensic strategy, identify propositions
- this is all pre-submission
3 - service delivery, forensic examination, evaluates outcomes, interpretation and report
what is the hierarchy of propositions and give an example of this
- source (has semen originated from suspect)
- activity (has suspect had sexual intercourse with complainant)
- offence (did suspect rape the complainant)
what framework (5 things) does the CAI model provide for the investigator
1 - ensures requirements are clearly articulated
2 - assists in setting forensic examination strategy
3 - assists decision making
4 - provides staged information (Investigative or Evaluative phases)
5 - enhances value (cost/time vs. usefulness = value)
what framework (4 things) does the CAI model provide for the criminal justice system
1 - ensures a balanced (unbiased) approach
2 - ensures impartiality and transparency
3 - allows discussion of strength of evidence
4 - adds value (not to be confused with cost)
what is the 3 steps of the forensic process
1 - crime scene examination (investigation)
2 - laboratory examination (evaluation)
3 - court (adjudication)
what 5 things does CAI require
1 - excellent communication between all key parties
2 - clear understanding of each other’s requirements
3 - agreement of forensic examination strategy
4 - understanding of expected outcomes
5 - exploration of staged approach where possible
what is the equation for the posterior odds for the court
posterior odds = likelihood ratio x prior odds
(the court = the scientist x other info)
Pr(GIE)/Pr(ḠIE) = Pr(EIG)/Pr(EIḠ) x Pr(G)/Pr(Ḡ)
where
E = evidence
G = guilty
Ḡ = innocent
Pr = probability of
what framework (6 things) does the CAI model provide for the forensic scientist
1 - ensures clear understanding of case information and issues
2 - leads to an agreed forensic examination strategy
3 - defines propositions for testing
4 - enables staged examination and reporting
5 - is underpinned by sound statistical theory
6 - adds value to the scientist’s role
What are the principles of Bayes Theorem
- evaluation
- what scientist must do/be able to do
- likelihood ratio determines?
- evaluation must be carried out within a framework of circumstances (I or information)
- the scientist must make clear their understanding of the case circumstances relevant to the evaluation (conditioning information)
- scientist must consider their observations in the light of prosecution Hp and defence Hd propositions (propositions must be clearly stated and subject to change)
- scientist must consider the probability of their findings E if the prosecution/defence proposition were true
- relative magnitude of these two probabilities (LR) determines the assistance provided by their findings in weighing the two propositions against each other
What propositions are addressed?
What happens if expert can only address one proposition?
- address at least one pair of propositions based on prosecution issue and one based on alternative/defence issue
- 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 is the likelihood ratio?
- probability of the evidence given the prosecution hypothesis and background info divided by the probability of the evidence given the defence hypothesis and the info
- probability of the evidence if the prosecution version of events is true divided by the probability of the evidence if the defence version of events is true - all taking into account relevant contextual information
What is conditional probability?
- the likelihood of an event occurring 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 effect the probability of the other event occurring
