of using officially or routinely recorded data for estimating concurrent behavior that cannot be routinely measured.

On balance we felt it is helpful to limit the term "prediction" to future-oriented research. It is immaterial whether the data for the independent variables (predictors) are collected retrospectively at one time or longitudinally.

Classification research tends to focus on dividing individuals into distinctive subgroups. In traditional classification research (e.g., Gibbons, 1975), all persons being classified are to fall in a group defined by the research, and no one is to be classified as belonging to several groups. In others, a residual group of unclassified individuals is permitted,1 or persons are classified along several dimensions rather than in a single group (for example, as in the Diagnostic and Statistical Manual of Mental Disorders, Third Edition—Revised (DSM-III-R), American Psychiatric Association, 1987, discussed below).

By contrast, prediction research infrequently focuses on mutually exclusive subgroups, instead concentrating on estimating probabilities of future occurrences. In this framework, some or all persons could have probabilities greater than zero for several (or all) of the potential outcomes.

The purposes for undertaking classification are varied and may or may not be forward looking, whereas prediction is always forward looking by our definition. In the context of violence research, classification may be undertaken to estimate the prevalence of violent persons, or categories of violent persons, in specific populations; to construct typologies that assist in understanding personal and social characteristics of categories of violent and nonviolent persons; to learn more about causes, correlates, and stability associated with categories of violent persons; to diagnose individuals for purposes of planning treatment; and to assign individuals to groups for purposes of case management.2

The purposes of prediction may be similar, but prediction involves future behavior. Predictions of future violence may be made to determine whether subjects pose a risk to the community when released from criminal justice or mental health restraints; to investigate the causal relationships between events at two or more points in time; or to project future demands on criminal justice and health care resources.

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