Department of Homeland Security Bioterrorism Risk Assessment: A CALL FOR CHANGE by National Research Council of the National Academies

Author:National Research Council of the National Academies
Language: eng
Format: epub
Tags: Conflict and Security Issues : Prevention, Security and Response
Publisher: NATIONAL ACADEMY PRESS
Published: 2008-12-03T00:00:00+00:00

See also random variable, event space.

Term, with Synonyms, Cross-References, and DHS Lexicona Definitions

Committee’s Recommended Definition

Notes, Comments, and References

event space

The set of all possible outcomes of an experiment or of some (unknown) phenomenon. (After Feller [1968]g and Statistical Education Through Problem-Solving [STEP] Consortium.f)

Synonym: sample space

See also event.

event tree

A tree formed of a sequence of random variables, called events. The branching point at which a new variable is introduced in the tree is called a node. Each node is followed by the possible random variable realizations, called outcomes, and their probability distributions conditional on outcomes of previous random variables in the tree. The outcomes are represented as arcs leading from one event to the next. The joint probability of the intersection of events that constitute a sequence (or scenario) is found by multiplication. A natural way to construct an event tree is to place events in the chronological order in which they occur, if this order is known.l

An event tree is essentially a decision tree with the decisions removed or replaced by nodes representing events that are the result of probabilistic decisions (made either by the decision maker or some other agency). If a node in an event tree represents a decision taken by an adversary, then the (conditional) probabilities of the resulting events must be assessed or computed just as those for any other event nodes. Note that some computations (perhaps based on game-theoretic approaches) might produce event probabilities of 0 or 1, associated with “knowing” with certainty what action the adversary will take.

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