Expect.that.knowledge.uncertainty.will.never.be.reduced.to.zero..Know.that.natural. variability.will.never.disappear..These.two.simple.facts.mean.that.the.risk.characterization.from.your.risk.assessment.is,.at.best,.an.informed.estimate..At.worst,.it.may. be.well-intentioned.speculation..What.assessors.and.managers.both.need.to.know.is. that.the.outputs.of.a.risk.assessment.are.conditional.answers.based.on.the.data.and. data.gaps,.on.the.assumptions.and.estimation.tools,.and.on.the.techniques.and.methodologies.used.to.arrive.at.the.answers..They.also.need.some.idea.of.where.the.assessment.answers.lie.on.the.continuum.between.the.best.estimate.and.well-intentioned. speculation. A.simplistic.schematic.of.a.decision.situation.is.shown.in.Figure 16.1..A.risk.assess-

ment.has.several.inputs.that.include.knowledge,.data,.policy,.and.information.in.many. forms..Data. gaps. and. other. forms. of. uncertainty. are. ubiquitous. characteristics. of. these.inputs. Assumptions. made. to. help. address. uncertain. inputs. find. their. way. into. the.

model.and.affect.model.outputs,.e.g.,.risk.characterizations.and.the.like,.which,.in. turn,.influence.the.risk.management.decision..Any.methodologies.used.to.address. the. uncertainty. and. variability. in. inputs.will. result. in. a. similar. chain. of. events.. Likewise,.assumptions.made.about.the.model’s.structure.will.influence.outputs.and. decisions. Sensitivity.analysis.is.the.study.of.how.the.variation*.in.a.risk.assessment.output.