Expert Testimony - Midterm 1

Expert Psychological Testimony

An expert serves the court by translating reliable psychological knowledge into clear, practical guidance that laypeople can apply to disputed facts, and the expert's credibility depends on separating data from advocacy.

Clinical Expert

A clinical expert offers case-specific opinions about a person's present capacities or past mental state.

Social/Cognitive Expert

A social/cognitive expert typically educates the court about general mechanisms such as memory, suggestibility, or decision bias and then shows how those mechanisms are relevant to the case at hand.

Developmental Expert

A developmental expert evaluates whether a child can perceive events, remember them, and communicate truthfully, and the expert evaluates whether interview methods supported reliable recall or instead introduced suggestion.

Effective Testimony

Effective testimony begins with a plain-English bottom line, continues with concise method descriptions and concrete findings, and ends with explicit limits and alternative explanations, because jurors trust structured candor more than technical bravado.

Cross-Examination

You should treat cross-examination as a test of discipline where you answer exactly the question asked, decline to step outside your expertise, and reaffirm your limits, because most credibility damage occurs when experts overreach.

High-Quality Report

A high-quality report lists everything reviewed, justifies every tool used, explains why those tools are appropriate for this referral question, and provides opinion statements that are logically tethered to the presented facts.

Gatekeeping Function

The gatekeeping function exists to admit evidence that genuinely aids the trier of fact and to exclude opinions that are methodologically weak or likely to mislead, so you should always tie your method to recognized quality criteria.

Frye Standard

Under Frye, a method is admissible if it has gained general acceptance in a relevant scientific community, but this standard can entrench outdated views and invite disputes about which community counts, so it is necessary but not sufficient in assessing reliability.

Daubert Standard

Under Daubert and Rule 702, your testimony must rest on a method that can be tested, that has a known or knowable error rate, that has been subjected to peer review, and that is at least considered within the field, and your testimony must also be relevant and beyond common knowledge.

Joiner Standard

Under Joiner, courts should exclude opinions that make analytical leaps from modest data to sweeping conclusions, so you should show your inference chain step-by-step and avoid conclusory jump points.

Kumho Standard

Under Kumho, all expert testimony—not only laboratory science—must meet reliability expectations, so experience-based opinions must still be anchored to transparent criteria and error controls.

Mohan Standard

Under Mohan, Canadian courts ask whether proposed evidence is relevant, necessary to assist beyond the jury's common knowledge, not otherwise excluded, and offered by a qualified expert, so you should always justify why your testimony materially assists the trier of fact.

Improving Admissibility

You improve admissibility when you present published validation, transparent error metrics, inter-rater reliability, and external proficiency data, because these demonstrate that your method works in other hands and not only yours.

Jeopardizing Admissibility

You jeopardize admissibility when you claim absolute certainty, rely on untested novelty, or gloss over error and bias controls, because courts treat such claims as red flags for junk science.

Forensic Identification Evidence

Forensic identification includes DNA, latent prints, hair and fiber, tool marks and ballistics, footwear and tire impressions, and handwriting and document examination, and each discipline demands controls for contamination, subjectivity, and misleading phrasing.

System Variable

A system variable in forensic labs is a factor the lab can control—such as blind verification, contamination protocols, and proficiency testing.

Estimator Variable

An estimator variable is an inherent condition such as sample quantity, mixture complexity, or substrate distortion that cannot be changed after the fact.

Claim ladder

The safest way to report a comparison by moving from qualitative support to stronger empirical support.

Likelihood ratio

A statement of how much more probable the observed evidence is if the same-source hypothesis is true compared with the different-source hypothesis.

DNA analysts

Should describe mixture assumptions, drop-in and drop-out risks, laboratory error versus interpretation error, and random-match probabilities or likelihood ratios.

Fingerprint examiners

Should explain how ACE-V structures the work and why blind verification and proficiency tests reduce bias.

Tool-mark and firearms opinions

Should discuss subclass characteristics and wear, as these can create misleading similarity.

Bitemark and footwear comparisons

Require cautious language because skin deforms under pressure and wear patterns evolve.

Probability fallacies

Should be neutralized by clarifying that a low match probability does not equal a low probability of innocence.

Confessions

Are uniquely persuasive to jurors and can pull other evidence into their orbit.

Maximization tactics

Raise the perceived cost of denial by asserting certainty and exaggerating evidence strength.

Minimization tactics

Lower the perceived cost of confession by downplaying seriousness and offering face-saving themes.

False confessions

Fall into three categories: voluntary, coerced-compliant, and coerced-internalized.

Personal risks

Such as youth, intellectual disability, acute mental illness, severe fatigue, and intoxication amplify susceptibility.

Situational risks

Include long isolation, late-night interviews, and false-evidence ploys that tip decisions toward admission.

Contamination

Arises when non-public case facts enter a suspect's statement through disclosure or suggestion.

Best practice in interviews

Is to record the entire interview, limit duration, and document who introduced each detail.

Clear boundaries in interrogations

Classify threats, promises of legal benefit, and physical coercion as prohibited.

Human memory

Is reconstructive rather than photographic, altered by stress, weapon focus, and other factors.

Estimator variables

Factors such as lighting, distance, stress, cross-race, age, and retention interval that cannot be controlled after the event.

System variables

Procedural choices such as lineup type, instructions, administrator knowledge, filler selection, and feedback that law enforcement can control.

Simultaneous lineups

Encourage relative judgments in which witnesses choose the best available face, increasing false identifications when the culprit is absent.

Sequential lineups

Encourage absolute judgments and reduce false identifications, although they can slightly reduce correct identifications.

Lineup safeguards

Measures such as double-blind administration, standardized instructions, fillers matching the witness's description, and immediate verbatim confidence statements that reduce pressure, prevent cueing, and preserve diagnostic value.

Confidence

Can be informative when taken immediately after a fair procedure and before any feedback; however, post-identification feedback inflates confidence without improving accuracy.

Show-ups

Inherently risky as they present a single person, should be used only when exigency demands a quick on-scene check, and must be accompanied by strong instructions and immediate confidence capture.

Fitness or competency to stand trial

Answers whether the person understands the nature and object of the proceedings and can rationally assist counsel, using records, interviews, mental status examinations, malingerings screens, structured tools, and collateral.

Unfit person

Treatment or education aims to restore competence, pausing the case until the person can meaningfully participate.

Insanity or NCRMD

A retrospective evaluation of whether a mental disorder rendered the person unable to appreciate the nature or wrongfulness of the act at the time of the offence.

Fitness vs. insanity

Fitness concerns current procedural capacity, while insanity concerns past moral and cognitive appreciation, leading to different outcomes.

NCRMD findings

Managed through dispositions such as absolute discharge, conditional discharge, or hospital treatment with review, balancing public safety, treatment needs, and liberty interests.

Truth in ethics

Means you owe loyalty to the court's fact-finding rather than to a side, presenting unfavorable facts candidly.

Justification in ethics

Means opinions must rest on adequate data and reliable methods, showing validation, error rates, and proficiency rather than relying on personal authority.

Transparency in ethics

Means spelling out materials reviewed, methods used, assumptions made, and limits of inference for the trier of fact to follow and critique reasoning.

Reducing adversarial allegiance

Involves adopting standard operating procedures, seeking disconfirming evidence, using blind verification, and disclosing contrary literature to make the process robust to expectation effects.

Opining on legal issues

Should be avoided; instead, describe psychological facts and implications, as legal conclusions belong to the court.

Opening statement signaling reliability

The best opening statement should signal reliability to the jury.

Best opening statement

I was asked to evaluate the following question using these established methods, and I will explain not only my findings but also their limits.

Double-blind lineup administration

Double-blind administration is critical because unintentional cues can still shape a witness's choice, and removing administrator knowledge prevents both conscious steering and subtle nonverbal influence.

Likelihood ratio of 1

A likelihood ratio of 1 communicates that the evidence fits the same-source hypothesis and the different-source hypothesis equally well, so the evidence has no discriminating value on its own.

Essential instruction for lineups

This instruction is essential because it removes the implied demand to choose, which lowers relative-judgment errors when the culprit is absent from the lineup.

Fingerprint opinion phrasing

A fingerprint opinion should be phrased as 'the features provide strong support for a same-source inference under our lab's criteria and blind verification.'

Justification for show-up

A show-up is justified only when exigency demands a rapid on-scene assessment, and it should be framed with a clear statement that the person may or may not be the culprit.

Persuasive indicator of confession

The most persuasive indicator is the presence of accurate, non-public case details that the suspect volunteered before police disclosure.

Individualization claims

Courts prefer to avoid individualization claims because they imply unique source identity despite the lack of universally validated uniqueness models and quantified error.

Peer review and admissibility

Peer review alone is insufficient because it does not substitute for testability and error quantification.

Conveying uncertainty

An expert should convey uncertainty by stating the assumptions made, reporting quantitative weight where available, and explaining what new data would increase or decrease confidence.

High confidence rating after lineup

A high confidence rating measured immediately after a fair lineup can be informative because it captures memory strength before feedback or repeated testing distorts certainty.

Random-match probability

A random-match probability is not the probability that the suspect is guilty; it is the probability that a random, unrelated person would match the profile.

PEACE model

The PEACE model improves reliability because it emphasizes preparation and open-ended accounts rather than confrontation and confession seeking.

Cross-race recognition differences

Cross-race recognition differences are not system variables because they arise from the interaction of witness and target demographics, not from police procedure.

Transparency in methods

Transparency about materials, methods, and limits increases credibility, because it allows the trier of fact to audit your reasoning.

Prosecutor's fallacy

The prosecutor's fallacy mistakes a low match probability for a low probability of innocence, which flips the conditional and exaggerates the weight of evidence.

Defence attorney's fallacy

The defence attorney's fallacy dismisses strong evidence by pointing to a large population base without considering how case facts narrow the relevant pool.

Low-template DNA mixture

The observed profile is most consistent with a three-contributor mixture under low-template conditions.

Same-source hypothesis

It provides only moderate support for the same-source hypothesis for the named contributor.

Forensic match statistics

The features observed in the questioned and known samples are approximately one hundred times more likely if they originate from the same source than if they originate from different sources.

Interview duration

Interviews that exceed four hours increase fatigue, stress, and compliance pressures, all of which impair judgment and memory accuracy.

Investigative interview goal

The goal of an investigative interview is accurate information rather than endurance.

CST opinion sentence structure

In my opinion, the defendant currently understands the nature and object of the proceedings and can rationally assist counsel.

Blind verification

Blind verification is critical because it prevents the second examiner from being influenced by the first examiner's conclusion or by case context.

Independent examiners

When two independent examiners converge without knowledge of each other's judgments, the lab demonstrates that the conclusion is not a product of expectation effects.

Coerced-compliant confession

This statement is at high risk of being coerced-compliant or coerced-internalized because youth and overnight duration increase suggestibility.

Simultaneous lineup

Because the suspect stood out and the procedure was simultaneous, the witness was likely pushed toward relative judgment.

Post-identification feedback

The post-identification feedback likely inflated confidence, so the resulting identification has reduced diagnostic value.

Unique match claim

A unique match claim based on wear-sensitive features is unsafe because wear changes over time and subclass characteristics can mimic individuality.

Competency requirements

Competency requires both understanding and the rational ability to assist.

Paranoid delusions

Active paranoia that prevents collaboration indicates present unfitness.

Admissibility

Admissibility is the judge's determination that expert evidence is both helpful to the trier of fact and methodologically reliable.

Daubert/Rule 702

Daubert/Rule 702 is the reliability framework that requires testability, error awareness, peer review, and field consideration in addition to relevance beyond common knowledge.

Joiner

The principle that courts exclude opinions when conclusions leap beyond what the data can justify.

Kumho

The ruling that reliability expectations apply to all forms of expertise, including experience-based methods.

Mohan (R-N-E-Q)

The Canadian test requiring relevance, necessity, lack of exclusion, and a qualified expert.

Class Characteristics

Features that place an item in a broad category.

Individual Characteristics

Features claimed to be unique to a single source.

Individualization

A categorical claim of unique source that is rarely justified by validated uniqueness and quantified error.

ACE-V

The fingerprint workflow of Analysis, Comparison, Evaluation, and Verification.

Confirmation Bias

The tendency to see what we expect, which laboratories counter with blind procedures and proficiency testing.

Relative Judgment

The act of picking the closest face in a simultaneous lineup.

Absolute Judgment

The act of comparing each face to memory independently in a sequential lineup.

Confidence Statement

The witness's immediate, verbatim rating at the time of identification, which retains diagnostic value when collected before feedback.

Defence Fallacy

The error of dismissing strong evidence by citing population size without considering case-specific narrowing.

CST/FST

The present-tense capacity to understand proceedings and rationally assist counsel.

NCRMD/Insanity

The past-tense determination that a mental disorder prevented appreciation of the nature or wrongfulness of the act.