Wiley Handbook of Science and Technology for Homeland Security, 4 Volume Set

LOGIC TREES: FAULT, SUCCESS, ATTACK, EVENT, PROBABILITY, AND DECISION TREES

ROBIN L. DILLON-MERRILL

McDonough School of Business, Georgetown University, Washington, D.C.

GREGORY S. PARNELL

Department of Systems Engineering, United States Military Academy, West Point, New York

DONALD L. BUCKSHAW

Innovative Decisions, Inc., Vienna, Virginia

1 INTRODUCTION

This article provides an introduction to logic trees. Six types of logic trees are described, compared, and illustrated in this article: fault trees, success trees, attack trees, event trees, probability trees, and decision trees. Probabilistic risk analysis (PRA) models may include fault trees, success trees, attack trees, and event trees [1]. Decision analysis models generally include probability trees and/or decision trees [2]. We illustrate the different models using bioterrorism examples. Table 1 provides a summary of the different logic tree models. The table includes the uses, mathematical foundation, data required, advantages, and limitations.

2 FAULT, SUCCESS, AND ATTACK TREES

A fault tree is a graphical probabilistic risk assessment (PRA) technique whereby an undesirable event (called the top event) is postulated and the possible ways for this top event to occur are systematically deduced for combinations of initiating and intermediate events [3]. The events are generally binary (or Boolean), that is, events may or may not occur. System components are either in parallel or in series, so combinations of events that lead ...