Encyclopedia of Psychology and Law

proxy, families may debate about whom to appoint to

make treatment decisions on the patient’s behalf or

disagree about which course of action is best. Although

a mental health evaluator may participate in helping

clarify issues such as decision-making capacity, deter-

mining who acts as the surrogate decision maker and

establishing guidelines for decision making are usu-

ally left to the treating physician, hospital ethics com-

mittees, or even the courts.

Barry Rosenfeld and Lia Amakawa

See also Proxy Decision Making; Psychiatric Advance

Directives

Further Readings

American Medical Association Council on Ethical and

Judicial Affairs. (1998). Optimal use of orders not to

intervene and advance directives. Psychology, Public

Policy, and Law, 4,668–675.

Cruzan v. Director, Missouri Department of Health, 497 U.S.

261 (1990).

Emanuel, L. L. (1988). Regulating how we die: The ethical,

medical, and legal issues surrounding physician-assisted

suicide. Cambridge, MA: Harvard University Press.

In re Quinlan, cert. denied, 429 U.S. 92 (1976).

Rosenfeld, B. (2004). Physician-assisted suicide, euthanasia,

and the right to die: The interface of social science,

public policy, and medical ethics. Washington, DC:

American Psychological Association Press.

Vacco v. Quill, 521 U.S. 793 (1997).

Washington v. Glucksberg, 521 U.S. 702 (1997).

Werth, J., Benjamin, G., & Farrenkopf, T. (2000). Requests

for physician-assisted deaths: Guidelines for assessing

mental capacity and impaired judgment. Psychology,

Public Policy, and Law, 6(2), 348–372.

ESTIMATOR ANDSYSTEMVARIABLES

IN EYEWITNESSIDENTIFICATION

A distinction between estimator and system variables

is made in the eyewitness research literature between

two categories or types of variables that influence the

accuracy of eyewitness accounts. System variables are

those that are (or can be) under the control of the jus-

tice system, whereas estimator variables cannot be

controlled by the justice system. Examples of system

variables include factors such as the instructions given

to eyewitnesses prior to their viewing a lineup or the

number of people who are used in a lineup. Examples

of estimator variables include factors such as how

good a view the eyewitness had of the perpetrator dur-

ing the crime or whether the witness and perpetrator

were of the same or different race. The estimator ver-

sus system variable distinction tends to be tied to a

temporal unfolding of events, in the sense that events

that occur before or during the witnessing experience

are necessarily relegated to estimator variable status

whereas system variables begin to come into play

later, once the investigation is under way. There is no

presumption in the estimator variable versus system

variable distinction that one category of variables has

more impact on eyewitness accuracy than the other.

Nevertheless, this distinction, first articulated in 1978

by Gary L. Wells, has tended to result in a higher pre-

mium being placed on system variables because these

can be used to help minimize eyewitness errors in

actual cases, whereas estimator variables can only be

used to postdict how the variables might have influ-

enced the eyewitness.

The study of system variables has generally been

tied to policy-related recommendations on ways to

improve how crime investigators interview eyewit-

nesses and on ways to improve how lineups are con-

structed and conducted. The study of estimator

variables, in contrast, has more often been tied to the

development of expert testimony that can assist triers

of fact (e.g., judges, juries) in deciding whether to

accept the testimony of an eyewitness as having been

accurate or mistaken. In fact, however, system vari-

ables are as relevant to expert testimony as are esti-

mator variables, and in recent years, it has become

more apparent that estimator variables and system

variables are not independent. In general, the impact

of system variables is likely to depend somewhat on

the levels of the estimator variables. An obvious

example of this dependence is when the estimator

variables are highly favorable to the existence of an

extremely deep, solid memory. If memory is strong

enough, system variables would not likely have much

impact. For instance, system variable research shows

that it is critical for eyewitnesses to be warned prior to

viewing a lineup that the actual perpetrator might not

be present, because the absence of such a warning

leads eyewitnesses to select someone from a lineup

even if the actual perpetrator is not present. However,

if the eyewitness’s memory is strong enough (e.g.,

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