Definition(s)
Marginal Probability
Statistical distribution (probability) of the occurrence of a variable A that is obtained by integrating over all values of the other variables B, C, …
NOTE The marginal probability of A for all values of B, C, … is written as P(A). The concept is applicable to metocean parameters, as well as to actions and action effects.
EXAMPLE When considering wave conditions, A can be the individual crest elevation for all mean zero-crossing periods B and all significant wave heights C, occurring at a particular site.
Source: API RP 2MET, Derivation of Metocean Design and Operating Conditions, First Edition, November 2014. Global Standards
Marginal Probability
Marginal probability is the unconditional probability of event A, P(A). It is the probability of A regardless of whether event B did or did not occur. If B can be thought of as the event of a random variable X having a given outcome, then the marginal probability of A can be obtained by summing (or integrating, more generally) the joint probabilities over all outcomes for X.
Sample Usage: Analysts estimated the marginal probability of a water system contamination, irrespective of the source or type of contaminate.
Source: DHS Risk Lexicon, U.S. Department of Homeland Security, 2010 Edition. September 2010 Regulatory Guidance