RSS - Evaluative Writing

Question 1

probability

Answer 1

• measurement of that event will occur
• quantified as number between 0 and 1 where 0 = impossible and 1 = certainty

Question 2

what are 5 rules of probability?

Answer 2

1 - probability of any event will always be a number from 0 to 1
2 - when an event cannot occur, the probability will be zero
3 - when an event is certain to occur, the probability is one
4 - sum of the probabilities of all the outcomes in the sample is one
5 - probability that an event will not occur is equal to 1, minus the probability that the event will occur

Question 3

What are two factors needed to determine probability?

Answer 3

E - event whose probability is being considered
I - information available to assessor when probability of E is being considered

Question 4

Axiomatic laws of probability

Answer 4

• unquestionable
• all the probabilities must add up to 1 - the accused is either guilty or innocent (in England and Wales at least)
• there is no third option
• pG + pI = 1

Question 5

What two things can probability be?

Answer 5

• objective
• logical measure of chance where everyone would be expected to agree to the value of relevant probability
• subjective
• measuring strength of persons belief in particular proposition

Question 6

notation

Answer 6

• p(x) = 1
• where p = probability of
• where x - variable of interest

p (G I E) = probability of guilt given the evidence
p (I I E) = probability of innocence given the evidence

Question 7

Lucia De Berk

Answer 7

• nurse arrested in 2001 after death of baby in her care at a hospital in the Hague apparently from poisoning
• apparently investigators found what they thought was a trend of suspicious deaths among 13 patients treated by De Berk in previous 4 years
• 5 others almost died in ‘suspicious’ circumstances
• sentenced to life in prison
• testimony of statistician - odds were 342 million to one that it was a coincidence she had been on duty when all incidents occurred
• spent 6 years in prison
• De berk was accused of some deaths she wasn’t even present in the hospital for
• however probability never recalculated
• new probability still raised concern but out of 250k nurses a couple hundred would be expected to be involved in a set of circumstances like Lucia
• 1 in 1000 or 1 in 25
• acquitted in April 2010

Question 8

What are two sample types?

Answer 8

• recovered or questioned samples (sample of unknown origin)
• control or reference sample of known origin

Question 9

Purpose of substrate control

Answer 9

• used to distinguish between environment and surroundings and enable us to differentiate these against the questioned samples

Question 10

Define relative frequency

Answer 10

• it is calculated against the items observed over a period of time in a laboratory or from all the DNA profiles in some defined population
• e.g. the Glass submitted for analysis is seen in approximately 7% of reference glass exhibits examined in this laboratory over the past five years”

Question 11

what should expert assessment of likelihood of obtaining particular findings be formed upon?

Answer 11

• formed upon data relevant to the type of evidence in question:
• extensive surveys, databases or experimentation
• or refer to the experts personal experiences and previous casework

Question 12

What is likelihood ratio

Answer 12

• relative value of
• likelihood of the evidence if the prosecutions proposition is true and the likelihood of the evidence if the defence proposition is true

Question 13

Define base rate

Answer 13

• background rates or prior odds
• A priori
• it is the relative frequencies of variables in the general population

Question 14

Bailes case study

Answer 14

• Alan Bailes lost his job when he was asked to take a saliva test which came back positive for cocaine
• he insisted he had never taken any but he lost is job for gross misconduct
• him and his family found news article to say 11 % of UK banknotes have cocaine on them
• on day of test he handled several hundred pounds of case
• he did not wash his hands before test which increased likelihood of drug being transferred from cash to his hands to swab

Question 15

base rate fallacy

Answer 15

• making a probability judgement based on conditional probabilities without taking into account the prior probabilities (prior odds)

Question 16

What can likelihood of evidence sometimes be related to?

Answer 16

• frequency of occurrence

Question 17

Suppose that a footwear mark taken from the crime scene is said to match the sole of a shoe in the suspect’s possession
- probability of finding this evidence (of match) of the shoe mark based on the prosecutions hypothesis will be in the order of…
- probability or likelihood of finding the evidence of match if another shoe made the mark (the defence proposition) will be more in the order of…
- what might we want to know

Answer 17

• one
• zero
• base rate
• whether or not a good proportion of the burglars in the area wear the same type of shoe?

Question 18

What are three expressions?

Answer 18

• percentage
• proportion (relative frequency)
• probability of likelihood

Question 19

What is important whenever we use these three expressions?

Answer 19

• inspect the basis on which the subjective assessment has been made

Question 20

Semantic scale

Answer 20

• sometimes expressed verbally using a semantic scale:
• moderate, weak, strong, very strong support etc.

Question 21

Bayes theorem considers…

Answer 21

• prior probability (odds) and the likelihood ratio for both pieces of evidence to produce the posterior odds

Question 22

the posterior odds in favour of the prosecution proposition are equal to?

Answer 22

• the product of
• the ratio of the probability of the evidence if the prosecution’s proposition is true to the probability of the evidence if the defence proposition is true
• and
• the prior odds in favour of the prosecution proposition

Question 23

Reed and reed

Answer 23

• David and Terence reed were convicted for murder of Peter Hoe
• peter has been repeatedly stabbed
• two pieces of plastic thought to be parts of two separate knife handles were found near to Peter’s body
• one had cellular material on it which matched David and peter and other had cellular material which matched Terence and another
• match probabilities were such that it was accepted to be their DNA
• one of the pieces of plastic fitted the blade of a knife which is found in a drain at Peter Hoes address
• cell site analysis put both reed and reed in vicinity of Peter’s address about the time
• Terence also purchased another identical tracksuit top on the day following the killing (prosecution contend this was because the other garment was heavily blood-stained
• lots of motive for brother to attack peter hoe
• DNA could have been transferred by primary, secondary or tertiary transfer
• recent appeal was directed towards challenging the admissibility of evidence given by Valerie Tomlinson (FSS) as to the manner and timing of the transfer of the appellants DNA AND the overall reliability of LTN DNA
• piece of plastic had visible traces of blood on it since it was on part of a blood-stained carpet
• a different piece of plastic had no traces of blood
• VT said test other plastic for DNA using LTN process
• two knife handle fragments with a profile of one of the reed’s - they were also foreign to scene as handles did not match any in Peter Hoe’s kitchen
• VT opinion that DNA transferred through primary transfer
• cell site analysis located offenders by their mobile phones
• appellant criticised her evidence
• she had failed to take account that the material was found only on a fragment of each handle
• she did not take into account the possibility that there might have been cellular material from others on the rest of the handle or on the blade
• Dr Budwole (FBI)
• evidence not accepted given that a properly qualified expert cannot evaluate the enumerate of possibilities of the circumstances of transfer
• in other circumstances an expert could give evaluative evidence
• he didn’t have enough info to assess the other possibilities

Question 24

What biological material can DNA sample originate from?

Answer 24

• bone
• hair
• vomit
• faeces
• skin flakes
• stains of biological fluid

Question 25

What are biological fluid stains detectable by?

Answer 25

• visual examination or presumptive test
• blood saliva semen
• sweat, skin cells, vaginal secretions - not detectable

Question 26

What happens if it is not detectable by visual examination or presumptive test

Answer 26

• not possible to know precise nature of biological material from which the DNA originated
• material often originates from skin cells, hence expression touch DNA

Question 27

Study undertaken by Lowe et al at FSS (tendency to deposit DNA, secondary transfer, mixed profile)

Answer 27

• in tests and control conditions there was difference between tendency of individuals to deposit or shed DNA but it was not known why this was so
• secondary transfer resulting in only the cellular material of the original transfer found could only occur under certain ideal conditions where clean objects and washed hands are used
• it would therefore be expected that unless the contacts have occurred within a very short period of time, a mixed profile will be found

Question 28

Professor Jamieson

Answer 28

• forensic institute
• not accredited by UKAS or any other body
• limited experience in DNA interpretation
• it is not understood how he had sufficient expertise to be able to give evidence in R v Hoey case let alone assist in attach made in that case on LCN process
• has given evidence in many low template DNA cases since then

Question 29

Source level propositions
- explain what limited to
- what doesn’t it consider
- what does it require little of

• give two examples

Answer 29

• limited to addressing whether or not apiece of evidence came from a particular source
• do not say anything about how the evidence came to be at the scene or on the defendant’s clothing
• do not take into account variables such as quantity, position, or distribution of the recovered material
• assessment of evidence under source level propositions require little in the way of circumstantial information
• defendant is/isn’t source of semen at scene

Question 30

Sub-source level propositions
- 3 examples

Answer 30

• DNA recovered from crime sample came from Mr Smith/didn’t come from Mr Smith/ come from some other person

Question 31

Activity level propositions
- 3 examples

Answer 31

• defendant had intercourse with victim
• defendant walked on carpet in burgled house
• defendant smashed the window

Question 32

Offence level propositions
- 3 examples

Answer 32

• defendant raped the complainant
• defendant burgled the house
• defendant committed criminal damage

Question 33

What must be noted about offence level propositions

Why can’t expert witnesses testify to propositions at the offence level

Answer 33

• they make conclusions about criminal responsibility and liability
• referred to as ultimate issue
• court must deal with this
• they involve factual and moral judgements that forensic scientists are not jurisdictionally competent to make e.g. did the victim consent, was harm caused unlawfully

Question 34

Where the scientist can say that the source of DNA came from a particular body fluid. What terminal we use here?

Answer 34

• attributable