Encyclopedia of Psychology and Law

attempting to pick one’s own mother from a lineup),

the presence or absence of this warning is of little con-

sequence. Hence, a complete understanding of eye-

witness performance clearly requires research on both

system and estimator variables.

Generally, system variables can also serve the

function of being estimator variables, but estimator

variables cannot be system variables. In some cases,

however, variables that traditionally have been con-

sidered estimator variables have taken on system-

variable-like properties. The confidence of an

eyewitness, for instance, has traditionally been con-

sidered an estimator variable because it was pre-

sumed to be beyond the control of the justice system,

and the emphasis of the estimator variable research

on eyewitness confidence was to find out how well or

poorly it postdicted the accuracy of the eyewitness.

Now, however, there is a great deal of research show-

ing that procedures that are under the control of the

justice system affect the confidence of the eyewitness

and the magnitude of the confidence-accuracy rela-

tion. In this sense, eyewitness confidence, tradition-

ally an estimator variable, has taken on some of the

properties of a system variable.

In eyewitness identification research, system and

estimator variables have been further subdivided in

recent years into two types—namely, suspect-bias

variables and general-impairment variables. Suspect-

bias variables are those that influence the eyewitness

specifically toward identifying the suspect from a

lineup, whereas general-impairment variables simply

reduce the overall performance of the eyewitness. An

example of a general-impairment system variable is

when the lineup administrator fails to instruct the eye-

witness that the perpetrator might not be in the lineup.

In this case, the instruction failure impairs the eyewit-

ness’s performance (by making the eyewitness insen-

sitive to the possibility that the correct answer might

be “not there”) but does not specifically bias the eye-

witness toward the suspect any more than it biases the

eyewitness toward the nonsuspects in the lineup. An

example of a suspect-bias system variable is when a

lineup is structured in such a way that the suspect

stands out as the obvious choice (e.g., as the only one

who fits the description of the culprit). An example of

a general-impairment estimator variable is poor view-

ing conditions at the time of witnessing. Poor viewing

conditions might impair the eyewitness’s performance

on the lineup, but poor viewing conditions do not

specifically bias the eyewitness toward the suspect

any more than they bias the eyewitness toward the

nonsuspects in the lineup. An example of a suspect-

bias estimator variable is when the eyewitness has

source confusion, such as when an innocent suspect is

picked out of a lineup because he was familiar; but he

was familiar because he had been a customer, not

because he was the person who robbed the clerk.

Gary L. Wells

See also Expert Psychological Testimony; Identification

Tests, Best Practices in

Further Readings

Wells, G. L., Memon, A., & Penrod, S. (2006). Eyewitness

evidence: Improving its probative value. Psychological

Science in the Public Interest, 7,45–75.

Wells, G. L., & Olson, E. (2003). Eyewitness identification.

Annual Review of Psychology, 54,277–295.

ETHICALGUIDELINES ANDPRINCIPLES

Ethicsis a term used to describe the guiding philoso-

phies and/or moral values of a group or an individual.

Although ethics are by definition theoretical in nature,

they are the underlying principles that help guide the

conduct of any given society, profession, or individual.

This entry reviews important concepts for under-

standing the application of ethical principles to the

practice of forensic psychology. It addresses issues

such as identifying the intended beneficiary of foren-

sic services, the application of the principle of benef-

icence/nonmalfeasance, and the relevance of existing

professional standards and guidelines. It then summa-

rizes four of the major elements of ethical forensic

psychological practice: competency, judgment, respon-

sibility,and accountability.

Intended Beneficiary of the

Forensic Product or Service

A critical aspect of ethical practice is the clarification

of the forensic task(s) to be provided and the acquisi-

tion of informed consent from the intended recipi-

ent(s) of those services, which should occur prior to

providing forensic services. This includes clarification

of at least the following areas:

258 ———Ethical Guidelines and Principles

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