Exam 2-Forensic Psych

Reliability

consistency or repeatability of a measure or observation

Test-retest reliability

degree to which a measure yields the same results over time

interrater relaibility

degree to which two or more observers or analysts independently arrive at the same measurement

validity

technique measures what it is supposed to measure

How is DNA evidence tested?

electropherogram - visual display of alleles and loci

• 2 alleles at each locus

• height of peak at different loci

if trace does not match source, it could be:

1. samples from different individuals

2. trace was contaminated

DNA is:

1. Reliable and valid method

2. Most objective (relies on computers)

3. Based on solid scientific foundation

Limitations of fingerprint evidence

- Fingerprints are not in the computer database

- Uncertain that “no 2 fingerprints are identical”

- Latent print quality

False positive

- “false alarm”

- Forensic analysts usually fall under false positives when determining a match

Confirmation bias

If I deem something to be true, I will then seek evidence to confirm it and ignore the evidence that does not support the hypothesis

Evidence of questionable validity

- Do two bullets match?

- Can tools leave signature patterns that can be matched?

- Can trace hairs be matched to a source?

- Can a bite mark be matched to teeth?

4 ways of communicating a match

• Qualitative statement – subjective statement about the strength of the match

  • E.g. source attribution to a reasonable medical certainty

• Simple match – statement that the tract and source share certain characteristics

• Match plus statistics – statement that incorporates statistics that place the match in context

• Individualization – match is so detailed that the trace could have only come from one person

strategies for communicating the nature of a match

• How often are forensic analysts wrong when they determine a match?

  • Especially rate of false positive

  • Difficult to calculate for most types of trace evidence

• Do not allow claims of professional experience to substitute for solid scientific foundation

• “Match” implies close correspondence

  • “Consistent with” may be a better term

• 2016 department of justice directed experts to stop using “to a reasonable degree of scientific certainty”

Profiling

• Process of drawing inferences about a criminal’s personality, behavior, motivation, and demographic characteristics based on crime scenes and other evidence

1. Pioneered by FBI’s Behavioral Science Unit

2. Involves understanding offender and victim

3. Largely unvalidated techniques

Signature

• distinctive, personal feature of the crime that presumably reveals the killer’s personality

1. Seen as the “why” or the crime

Characteristics of white make serial killers of average intelligence

• Suffer from brain injury that impairs rational thinking

• Abused in childhood

• Maladaptive behaviors in childhood

  • Killing animals

• Seek to dominate victims

• Prefer more intimate methods of murder

  • Stabbing, strangulation, etc.

• Interest in violent pornography

  • Murder is highly sexualized

• Victims tend to all be a certain type

  • Specific hair color, body type, race, etc.

• Replay killings for sexual stimulation

  • Taking clothes, hair

Organized serial killers

• Carefully select, stalk, and plan

• Demonstrate patience and self-control

• Clean up evidence after murder

• Use more elaborate rituals

  • E.g. torture or dismemberment

Problem with Holmes & Holmes (2010) classifications

most serial killers do not fall neatly into one of these categories

Visionary

psychotic, hears voices, see visions

Mission-oriented

kill people they believe are evil

Hedonistic

kill others for thrill and sadistic sexual pleasure

Power-oriented

get satisfaction from victim capture and control before killing

Effectiveness of profiles

• Very little research on effectiveness of profiles

• Study of 184 detectives found:

  • Most said profiling was helpful

  • 2.7% of profiles led to identifying the perpetrator

• Profilers’ accuracy rates generally less than 50%

• No discernible demographic resemblance between criminals who committed very similar crimes

  • May cause investigators to look for wrong type of person

3 stages of memory

1. Encoding – gathering information and putting it into a form that can be held in memory

• Imperfect encoding

2. Storage – holding encoded information over time

• Deterioration over time

3. Retrieval – accessing and pulling out stored information

• Retrieval distortion

Loftus (1984)

• 347 cases where the only evidence was an eyewitness

  • 74% convicted

  • 49% there was only 1 eyewitness

Cross-racial identification

• Cross-race accuracy is worse than within-race accuracy

• Begins around 9 months old

• Misidentification is about 1.5 times more likely

Relationship between stress and accuracy

Flashbulb memory

Stress negatively affects accuracy

1. Fear for one’s own safety

2. Weapon focus effect

   1. Further impairs recognition

Relationship between confidence and accuracy

• Highly correlated with persuasiveness

• Weakly correlated with accuracy

• Witness investment in identification correctness increases over time

Loftus and Palmer (1974)

• “Ran the stop sign” – 53% vs 35%

• “Did you see the broken headlight” – 2x more likely to say yes instead of using a broken headlight

• “smashed” vs. “contacted” – 41 mph vs 31 mph

Contextual bias

tendency for extraneous influences in the immediate environment to taint one’s judgment

1. E.g. seeing a gory crime scene, being told a suspect confessed

2. Especially in cases where latent print is not clear

Fingerprint evidence

1. 1892: Francis Galton described fingerprints

2. 1901: conviction on basis of fingerprint evidence

3. Friction ridges – swirling lines on fingertips

   1. Helps to create friction and allows us to better grasp objects (loop, swirl, arch)

How is fingerprint evidence produced?

• Latent prints – fingerprints found on a surface at the scene of a crime

  • Enhanced using powder, special lights, and magnification

• Potential matches are narrowed by a computer

  • BUT human examiner makes the final decision

Limitations of fingerprint evidence

• Fingerprints are not in the computer database

• Uncertain that “no 2 fingerprints are identical”

• Latent print quality

Matching is done by comparing ridge characteristics

• Bifurcations: single ridge splits into two

• Ends: ridge stops

• Crossovers: two ridges joined by a bridging ridge

• Independence: short ridges with clear end points

Ways to reduce bias and error in forensic testing

• A solid scientific foundation demonstrating the validity of an identification technique is a precondition for trustworthy analysis

• Ensure proper handling of trace evidence

• Retest trace evidence on routine basis

• Institute blind proficiency testing and certification of forensic analysts

• Designate evidence as property of legal system

  • Rather than property of prosecution

Post-identification feedback effect

• Tendency for biased feedback to distort the memory of eyewitnesses

  • Ex. Remember having a better view of the criminal, making the identification more easily, having paid more attention to the crime

Cognitive dissonance

When our actions and thoughts/feelings are not in harmony

1. Causes discomfort

2. Change one so that they are in alignment

Ways to improve eyewitness identification

1. pre-lineup interview

2. evidence-based grounds for putting suspects in lineups

3. blind lineup administrator

4. unbiased lineups

5. bias-reducing instructions

Pre-lineup interview

1. Should be conducted as soon as practical and recorded

2. Include eyewitnesses’ verbal description and information about prior familiarity with the culprit, self-reports about level of attention, and viewing conditions at the time of the crime

3. Use open-ended questions and avoid suggestive or leading questions

4. Instruct witness not to discuss crime with other witnesses or search the internet for photos

evidence-based grounds for putting suspects in lineups

Use documented evidence-based grounds to suspect an individual is guilty of specific crime being investigated

• Avoidance of culprit-absent lineups

Blind lineup administrator

decreases unintentional communication of suspect

Unibased lineups

1. Suspect does not stand out from the fillers

2. At least 5 fillers

3. Mock witness test

Bias-reducing instructions

1. The true criminal may not be in the lineup

   1. Remove pressure to pick someone

2. Person conducting lineup does not know who the suspect is

   1. Discourages looking to others for clues

3. If they feel unable to decide, they have the option of responding “don’t know”

4. After deciding they will be asked to state how confident they are in that decision

5. The investigation will continue even if no identification is made

6. Confidence ratings

   1. Confidence is likely to change between lineup and trial

   2. Take rating immediately after lineup

   3. High confidence is correlated with accuracy

      1. If lineup is unbiased

7. Video record lineup identification

   1. Including pre-lineup instructions and witness confidence statement

8. Avoid show ups

   1. Highly suggestive that one person is culprit

9. Avoid repeated identification procedures with the same witness and suspect

   1. First exposure to a suspect increases the probability that witness will identify the suspect as the culprit in the second

10. Expert testimony (like a psychologist) on eyewitness identification

11. Sensitizes jurors to the:

    1. Viewing and lineup conditions that compromise or enhance accuracy

    2. Relationship between witness confidence and accuracy