Because.risk.analysis.focuses.on.decision.making.under.uncertainty,.we.must.clearly. understand.what.uncertainty.is..At.the.most.basic.level,.when.we.are.not.sure,.then. we.are.uncertain..Uncertainty.arises.at.two.fundamentally.different.levels..First,.there. is.the.macrolevel.of.uncertainty..We.all.make.decisions.in.a.changing.and.uncertain. decision. environment.. This.means. the. systems,. processes,. social. values,. and. outcomes.of.concern.to.us.may.be.uncertain..Second,.there.is.the.microlevel.of.uncertainty..This. is. the. uncertainty. that. pertains. to. specific. decision. contexts. and. their. relevant.knowledge,.data,.and.models..These.latter.uncertainties.receive.most.of.the. attention.in.risk.assessment. If.there.was.no.uncertainty.there.would.be.no.question.about.whether.or.when.a.