ABSTRACT
Risk.analysis. is.decision.making.under.uncertainty..Resolving.and.addressing. that. uncertainty.is.a.primary.reason.for.risk.assessment..Probability.is.the.language.we. use.to.express.our.uncertainty..Someone.has.to.understand.probability.if.risk.assessment. is. going. to. address. the.knowledge.uncertainty. and.natural. variability. in. our. decision.problems..Quantitative.risk.assessment.uses.the.language.of.probability,.and. it.is.essential.to.know.the.structure.of.any.language.so.we.do.not.misuse.it..Learning. that.basic.structure.is.the.purpose.of.this.chapter. Risk. has. been. described. as. the. product. of. a. consequence. and. its. probability..
Assessors.need.to.understand.probabilities.to.assess.them.honestly..Managers.need. to.understand.probability. to.manage.risks.effectively..Risk.communicators.have. to. understand.probability. to.explain. it. to.others..Not.everyone.needs. to.know.how.to. do.good.probabilistic.risk.assessment,.but.everyone.does.have.to.be.conversant.and. knowledgeable.about.some.very.basic.facts.about.probability. One.problem.with.probability.is.that.it.does.not.lend.itself.well.to.intuition..If.there.
is.a.10%.chance.of.rain.and.we.get.caught.in.a.downpour,.we.are.more.inclined.to. think.the.forecast.was.wrong.than.we.are.to.think.the.rain.was.an.event.that.had.only. a.10%.chance. To.further.illustrate.the.nonintuitive.nature.of.probability,.consider.the.so-called.
