手法を比較

	Probabilistic Risk Assessment (PRA)	イベントツリー解析 (ETA)
分野	Disaster Studies	信頼性
系統	Process / pipeline	Process / pipeline
提唱年	1981	2002
提唱者	Kaplan & Garrick (risk triplet); Rasmussen WASH-1400; codified in NASA PRA Guide	Andrews & Moss
種類	Scenario-based quantitative risk model with uncertainty	Forward inductive logic tree
原典	Stamatelatos, M., Dezfuli, H., et al. (2011). Probabilistic Risk Assessment Procedures Guide for NASA Managers and Practitioners (2nd ed.), NASA/SP-2011-3421. NASA, Washington, DC.	Andrews, J. D., & Moss, T. R. (2002). Reliability and Risk Assessment (2nd ed.). Professional Engineering Publishing. ISBN: 978-1-86058-290-5
別名	Probabilistic Safety Assessment, PSA, Quantitative Risk Assessment (PRA), Probabilistic Risk Analysis	ETA, Event Sequence Diagram Analysis, Initiating Event Analysis, Olay Ağacı Analizi
関連	3	2
概要	Probabilistic Risk Assessment is the comprehensive, quantitative method for analyzing risk in complex engineered systems by answering three questions: what can go wrong, how likely is it, and how bad would it be. Kaplan and Garrick's 1981 paper gave the field its enduring definition of risk as a set of triplets — scenario, frequency, and consequence — and showed how to extend that definition to incorporate uncertainty through probability distributions. The NASA Probabilistic Risk Assessment Procedures Guide (NASA/SP-2011-3421) operationalizes this framework for high-consequence aerospace systems, combining initiating-event analysis, event trees and fault trees, consequence modeling, and formal uncertainty propagation into an integrated assessment. Unlike qualitative hazard identification, PRA produces a quantified risk picture — typically a frequency-of-exceedance curve with explicit uncertainty bounds — that supports decisions about where scarce safety resources will reduce risk most.	Event Tree Analysis (ETA) is a forward inductive technique used in reliability and risk engineering to model the possible outcomes that follow an initiating event. Starting from a single undesired event, ETA traces all subsequent event sequences through a binary branching tree representing the success or failure of safety barriers and protective systems. Introduced formally in reliability and risk literature by Andrews and Moss (2002), it is widely applied in nuclear, chemical, and aerospace industries to quantify accident sequence probabilities and guide safety decision-making.