Exam 1 (4)

Question 1

What distinguishes science?

Answer 1

-Scientific method
-Reproducible
-Instruments
—Reliability- consistency of an instrument
—Validity- does it assess what it says it assesses

Question 2

What is forensic evidence?

Answer 2

-Evidence relating to law
-Might be scientific but it might not be

Question 3

Why does good forensic evidence matter?

Answer 3

It contributes to wrongful convictions

Question 4

Examples of trace evidence

Answer 4

Hair, clothing fibers, tool marks, tire treads, bite impressions, skin cells, blood, saliva, semen, etc

Question 5

Class characteristics

Answer 5

-Common to a category
-Ex. Red trilobal fibers common from Honda Accords

Question 6

Individual characteristics

Answer 6

-“Unique” to that person/object
-Ex. Tool had a defect on it so we know its from Morgan

Question 7

Communicating similarity- qualitative statements

Answer 7

-Relative strength of match
-“The bite mark left on the victim strongly matches the defendant”
-Have no scientific meaning and no standards

Question 8

Communicating similarity- simple match

Answer 8

-Two samples share characteristics
-“Glass found on the defendant is consistent with the glass found at the crime scene”
-Most objective and fair

Question 9

Communicating similarity- match plus statistics

Answer 9

-Stats that help contextualize the match evidence- rare/common
-“The size 10 shoe impression left at the crime scene matches with the defendant’s show size. Over 5 million people in the US wear size 10”
-Word match implies 100% certainty

Question 10

Community similarity- individualization

Answer 10

-“…to the exclusion of all others”
-Ex. Mark on car could have only come from a screwdriver

Question 11

Communicating similarity- excluded

Answer 11

-Large differences between samples
-“This hair belongs to someone else”

Question 12

Communicating similarity- inconclusive

Answer 12

-Evidence is contaminated, incomplete, or cannot be analyzed
-“This hair evidence has been contaminated”

Question 13

Problems with classifying “matches”

Answer 13

-Conclusions drawn vary depending on the type of evidence and specific forensic evaluator
-Many statements are highly subjective and meaningless
-Exaggerated claims
-Error rates, false positive rates, etc are usually not known in cases
-Jurors can not understand the evidence
-Jurors can falsely perceive match is certain

Question 14

DNA short tandem repeats

Answer 14

-When a pattern of one or more nucleotides is repeated directly adjacent to each other
-Ex. CTTC CTTC CTTC —> affects gene expression

Question 15

DNA as evidence (gold standard)

Answer 15

-If two samples are not exactly the same, that person is excluded as the source
-If two samples are the same, then certain stats can be calculated

Question 16

Random match probability

Answer 16

-Probability that a randomly selected individual from the population would have the same DNA profile as the one found at the crime scene
—Frequencies in total population or specific populations
-Calculated by multiplying the frequencies of each allele at each STR locus (assuming alleles are independent)

Question 17

13-STR loci method

Answer 17

13 specific short tandem repeat (STR) locations on the genome are analyzed to create a unique genetic profile for an individual

Question 18

Communicating DNA as evidence

Answer 18

Based on pairs matching not an individual matching

Question 19

Likelihood ratio

Answer 19

-Ratio of the probability of obtaining the observed DNA evidence if the suspect is the source of the DNA to the probability of obtaining the same evidence if someone else is the source
-A higher likelihood ratio indicates a stronger support for the hypothesis that the suspect is the source of the DNA

Question 20

DNA as evidence- great but not perfect

Answer 20

-Mix of DNA
-Touch DNA is very easy to transfer
-Contaminated sample
-Degraded sample

Question 21

Fingerprints as evidence

Answer 21

-Lack of standardization
-Rarely given info on how rare/common certain ridge characteristics are
-Print quality matters
-Experience appears to matter
-Some studies suggest false positives could be low but false negatives could be much higher

Question 22

Other types of evidence (valid and reliable)

Answer 22

-Bullet striations, tool marks, bite marks
-Some info likely can be reliably and validly assessed like class characteristics, but in terms of matching they have a high false positive rate or we don’t know

Question 23

Confirmation bias

Answer 23

-Search out evidence that fits our opinion
—“The ridge looks close enough to that ridge”
-Discount evidence that doesn’t fit
—“That ridge doesn’t fit but that’s just an anomaly”

Question 24

Contextual bias

Answer 24

-Extraneous influences (emotions, expectations, motivations) causing erroneous decisions
-Ex. Info about the suspect’s criminal history

Question 25

Reducing error and bias

Answer 25

-Strict procedures -Do systematic research -Strict certification requirements -Random blind lab checks -Reduce certain communication between detectives and forensic examiners- evidence should be independent -Create a more neutrally motivated lab

Question 26

Are jurors well equipped in understanding offensive evidence and integrating all the info?

Answer 26

Particularly hard for low education jurors

Question 27

Do jurors adjust their guilt judgments based on probabilities presented in forensic evidence?

Answer 27

-Yes, but not enough -Incorrectly interpret probability statements (as % of guilt) -Same probabilities can be expressed differently —> prosecution/defense friendly

Question 28

What do jurors think of fingerprint evidence?

Answer 28

-They like it -Easy for jurors -Jurors are overconfident in fingerprint evidence