Expert Testimony

Clinicians participate in

1 Million cases annually

Jenkins v U.S. (1962)

ruled that psychologists qualify as mental health experts.

judges prefer…

psychiatrists as expert witnesses in hypothetical insanity cases.

Mental health experts must

• satisfy the judge that they have the proper credentials and that their knowledge is sound.

 PhD or PsyD, and they are licensed in the state

Frye Test

“[evidence] must be sufficiently established to have gained general acceptance in the particular field in which it belongs”

Evidence must exhibit

legal sufficiency

Legal sufficiency

the evidence is probative rather than prejudicial

Evidence must be relevant

it must pertain to the case presented

Evidence must be reliable

reliability in the legal sense has more to do with validity – we can depend on it

Daubert v. Merrell Dow Pharmaceuticals Inc. (1993)

Court ruled Frye standard be replaced by standards in the Federal Rules of Evidence

Determining Reliability: Daubert v Merrell Dow Pharmaceuticals include:

 Is the scientific theory capable of being tested?

 Does the test/technique have a known error rate?

 Has the theory or technique been subjected to peer

review?

 Is there general acceptance within the scientific

community about the theory or technique?

Criticisms of Daubert

Promotes role of judges as “gatekeepers” of what is science.

Kovera et al. (2002) found that judges

 cannot identify simple confounds in the design of studies

 don’t recognize the importance of a control group

judges were not very good at distinguishing between high-quality scientific research and flawed scientific research.

Psychologists may disagree about

whether a defendant has a mental disorder and whether that disorder affected their behavior at the time of the crime.

Problem 1

Psychologists often disagree on diagnoses

According to Faust and Ziskin, clinicians sometimes disagree more often than they agree.

Problem 2

People can fake symptoms (malingering)

Malingering means pretending to have a mental illness or exaggerating symptoms for personal gain, such as avoiding punishment.

Problem 3

Experts are often asked to reconstruct the past

A psychologist may evaluate a defendant months or even years after the crime occurred.

Do experts assist the judge or jury?

 Battle of the experts and “hired guns”

 Clinicians are poor judges of their accuracy

 They routinely demonstrate confirmation bias

 Clinicians get little feedback on their performance

 Jurors pay close attention to years of experience and

confidence – yet neither are related to performance

Conformation Bias

Tendency to look for support for your beliefs rather than search for disconfirming evidence.

Neitzel et al. (1999) findings includes…

• Experts do influence jurors.

• But the influence is not huge.

• Jurors are not simply doing whatever the expert says.

McCloskey & Egeth's Criticisms problem #1

1. The adversarial system can reduce objectivity

In court, each side hires its own expert.

As a result:

Experts may feel pressure to support the side that hired them.

This can create a "battle of the experts."

McCloskey & Egeth's Criticisms Problem #2

Experts know probabilities, but courts want certainty

Scientists usually think in terms of probabilities:

"The evidence suggests..."

or

"This is likely..."

McCloskey & Egeth's Criticisms Problem #3

Experts may exaggerate scientific agreement

Under pressure from attorneys, experts may make it seem like:

"All scientists agree with me."

when in reality there may be disagreement among researchers.

McCloskey & Egeth's Criticisms Problem #4

Experts are either too influential or not useful

McCloskey and Egeth argued there is a dilemma:

If jurors rely heavily on experts, the experts may have too much influence over verdicts.