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European Definition


Probability is the extent to which an event is likely to occur. [1]

European Project Definitions

CIPRNet project

The CIPRNet project [2] uses the following definition:

Probability is the measure of the chance of occurrence expressed as a number between 0 and 1, where 0 is impossibility and 1 is absolute certainty.

National definitions


Probability: In statistics, a measure of the chance of an event or an incident happening. [3]

Probabilité: Grandeur par laquelle on mesure le caractère aléatoire (possible et non certain) d’un événement par l’évaluation du nombre de chances d’en obtenir la réalisation. [4]


Probabilidad: Posibilidad de que algo ocurra bien sea que se haya definido, medido, o estimado objetiva o subjetivamente, o en términos de los descriptores generales (tales como raro, improbable, probable, casi cierto). La probabilidad puede expresarse cuantitativa o cualitativamente. [5]


Sandsynlighed er forekomsten af en bestemt hændelse udtrykt ved et tal mellem 0 og 1 (eller mellem 0 og 100%), hvor 0 betegner en fuldkommen usandsynlig forekomst og 1/100% en hel sikker forekomst. Se også hyppighed. [6]


Probabilidad: Define la posibilidad de que ocurra un evento o se dé un resultado. [7]
La probabilidad puede variar entre cualitativa, mediante descripciones de términos tales como posible o altamente confiado, a rangos cuantificados y cálculos únicos, según el nivel de comprensión de las causas de los eventos, series cronológicas históricas y condiciones futuras (DT 4). Refiérase también a riesgo.

United Kingdom (UK)

Probability is used to describe the chance or relative frequency of particular types of event occurring. [8]
It can also include sequences or combinations of such events.

United States

Likelihood that is expressed as a number between zero and one, where zero indicates that the occurrence is impossible and one indicates definite knowledge that the occurrence has happened or will happen, where the ratios between numbers reflect and maintain quantitative relationships. [9]

Standard Definition

ISO Guide 73:2009

Measure of the chance of occurrence expressed as a number between 0 and 1 where 0 is impossibility and 1 is absolute certainty. [10]

Other Definitions

Ontario (Canada)

Probability is the likelihood of an event occurring that may result in an emergency, disaster or service disruption. [11]

Probabilité: survenance prévisible d’un événement susceptible de causer une situation d’urgence, un sinistre ou une perturbation de services. [11]

See also


  1. ENISA Risk Glossary
  3. All Hazards Risk Assessment Methodology Guidelines 2012-2013, Public Safety Canada
  4. Guide Analyse de risques d'accidents technologiques majeurs (2002)
  5. Glosario Policia Colombia
  6. [HÅNDBOG I RISIKOBASERET DIMENSIONERING, Beredskabsstyrelsen, Denmark (2004)]
  7. Portal de Cambio Climático
  8. The National Adaptation Programme: Making the country resilient to a changing climate, UK Government (2013)
  9. DHS Risk Lexicon 2010 Edition, September 2010
  10. ISO Guide 73:2009
  11. 11.0 11.1 Province of Ontario’s Emergency Management Glossary of Terms