why we make bad decisions.docx

why we make bad decisions.docx

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whywemakebaddecisions

Whywemakebaddecisions?

DanGilbert,July2005

Weallmakedecisionseveryday;wewanttoknow whattherightthingistodo--indomainsfromthefinancial tothegastronomictotheprofessionaltotheromantic. Andsurely,ifsomebodycouldreallytellushowtodo exactlytherightthingatallpossibletimes, thatwouldbeatremendousgift.

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29Itturnsoutthat,infact,theworldwasgiventhisgiftin1738 byaDutchpolymathnamedDanielBernoulli.AndwhatIwanttotalktoyouabouttodayiswhatthatgiftis, andIalsowanttoexplaintoyouwhyitisthatithasn'tmadeadamnbitofdifference.

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46Now,thisisBernoulli'sgift.Thisisadirectquote. AndifitlookslikeGreektoyou,it'sbecause,well,it'sGreek. ButthesimpleEnglishtranslation--muchlessprecise, butitcapturesthegistofwhatBernoullihadtosay--wasthis:

 Theexpectedvalueofanyofouractions-- thatis,thegoodnessthatwecancountongetting-- istheproductoftwosimplethings:

 theoddsthatthisactionwillallowustogainsomething, andthevalueofthatgaintous.

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18Inasense,whatBernoulliwassayingis, ifwecanestimateandmultiplythesetwothings, wewillalwaysknowpreciselyhowweshouldbehave.

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26Now,thissimpleequation,evenforthoseofyou whodon'tlikeequations,issomethingthatyou'requiteusedto. Here'sanexample:

ifIweretotellyou,let'splay alittlecointossgame,andI'mgoingtoflipacoin, andifitcomesupheads,I'mgoingtopayyou10dollars, butyouhavetopayfourdollarsfortheprivilegeofplayingwithme, mostofyouwouldsay,sure,I'lltakethatbet.Becauseyouknow thattheoddsofyouwinningareonehalf,thegainifyoudois10dollars, thatmultipliestofive,andthat'smorethanI'mchargingyoutoplay.So,theansweris,yes. Thisiswhatstatisticianstechnicallycalladamnfinebet.

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03Now,theideaissimplewhenwe'reapplyingittocointosses, butinfact,it'snotverysimpleineverydaylife. Peoplearehorribleatestimatingbothofthesethings, andthat'swhatIwanttotalktoyouabouttoday.

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16Therearetwokindsoferrorspeoplemakewhentryingtodecide whattherightthingistodo,andthoseare errorsinestimatingtheoddsthatthey'regoingtosucceed, anderrorsinestimatingthevalueoftheirownsuccess. Now,letmetalkaboutthefirstonefirst. Calculatingoddswouldseemtobesomethingrathereasy:

 therearesixsidestoadie,twosidestoacoin,52cardsinadeck. Youallknowwhatthelikelihoodisofpullingtheaceofspades orofflippingaheads. Butasitturnsout,thisisnotaveryeasyideatoapply ineverydaylife.That'swhyAmericansspendmore-- Ishouldsay,losemore--gamblingthanonallotherformsofentertainmentcombined. Thereasonis,thisisn'thowpeopledoodds.

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02Thewaypeoplefigureodds requiresthatwefirsttalkabitaboutpigs. Now,thequestionI'mgoingtoputtoyouiswhetheryouthink therearemoredogsorpigsonleashes observedinanyparticulardayinOxford. Andofcourse,youallknowthattheanswerisdogs. Andthewaythatyouknowthattheanswerisdogsis youquicklyreviewedinmemorythetimes you'veseendogsandpigsonleashes. Itwasveryeasytorememberseeingdogs, notsoeasytorememberpigs.Andeachoneofyouassumed thatifdogsonleashescamemorequicklytoyourmind, thendogsonleashesaremoreprobable. That'snotabadruleofthumb,exceptwhenitis.

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40So,forexample,here'sawordpuzzle. Aretheremorefour-letterEnglishwords withRinthethirdplaceorRinthefirstplace?

 Well,youcheckmemoryverybriefly,makeaquickscan, andit'sawfullyeasytosaytoyourself,Ring,Rang,Rung, andveryhardtosaytoyourself,Pare,Park:

theycomemoreslowly.Butinfact,therearemanymorewordsintheEnglishlanguage withRinthethirdthanthefirstplace. ThereasonwordswithRinthethirdplacecomeslowlytoyourmind isn'tbecausethey'reimprobable,unlikelyorinfrequent. It'sbecausethemindrecallswordsbytheirfirstletter. Youkindofshoutoutthesound,S--andthewordcomes. It'slikethedictionary; it'shardtolookthingsupbythethirdletter. So,thisisanexampleofhowthisideathat thequicknesswithwhichthingscometomind cangiveyouasenseoftheirprobability--

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30howthisideacouldleadyouastray.It'snotjustpuzzles,though. Forexample,whenAmericansareaskedtoestimatetheodds thattheywilldieinavarietyofinterestingways-- theseareestimatesofnumberofdeathsperyear per200millionU.S.citizens. Andthesearejustordinarypeoplelikeyourselveswhoareasked toguesshowmanypeoplediefromtornado,fireworks,asthma,drowning,etc.Comparethesetotheactualnumbers.

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54Now,youseeaveryinterestingpatternhere,whichisfirstofall, twothingsarevastlyover-estimated,namelytornadoesandfireworks. Twothingsarevastlyunderestimated:

 dyingbydrowninganddyingbyasthma.Why?

 Whenwasthelasttimethatyoupickedupanewspaper andtheheadlinewas,"BoydiesofAsthma?

" It'snotinterestingbecauseit'ssocommon. It'sveryeasyforallofustobringtomindinstances ofnewsstoriesornewsreelswherewe'veseen tornadoesdevastatingcities,orsomepoorschmuck who'sblownhishandsoffwithafireworkontheFourthofJuly. Drowningsandasthmadeathsdon'tgetmuchcoverage. Theydon'tcomequicklytomind,andasaresult, wevastlyunderestimatethem.

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36Indeed,thisiskindofliketheSesameStreetgame of"Whichthingdoesn'tbelong?

"Andyou'rerighttosay it'stheswimmingpoolthatdoesn'tbelong,becausetheswimmingpool istheonlythingonthisslidethat'sactuallyverydangerous. Thewaythatmoreofyouarelikelytodiethanthecombination ofallthreeoftheothersthatyouseeontheslide.

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55Thelotteryisanexcellentexample,ofcourse--anexcellenttest-case ofpeople'sabilitytocomputeprobabilities. Andeconomists--forgiveme,forthoseofyouwhoplaythelottery-- buteconomists,atleastamongthemselves,refertothelottery asastupiditytax,becausetheoddsofgettinganypayoff byinvestingyourmoneyinalotteryticket areapproximatelyequivalenttoflushingthemoney directlydownthetoilet--which,bytheway, doesn'trequirethatyouactuallygotothestoreandbuyanything.

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23Whyintheworldwouldanybodyeverplaythelottery?

 Well,therearemanyanswers,butoneanswersurelyis, weseealotofwinners.Right?

Whenthiscouplewinsthelottery, orEdMcMahonshowsupatyourdoorwiththisgiantcheck-- howthehelldoyoucashthingsthatsize,Idon'tknow. WeseethisonTV;wereadaboutitinthepaper. Whenwasthelasttimethatyousawextensiveinterviews witheverybodywholost?

 Indeed,ifwerequiredthattelevisionstationsrun a30-secondinterviewwitheachloser everytimetheyinterviewawinner,the100millionlosers inthelastlotterywouldrequirenine-and-a-halfyears ofyourundividedattentionjusttowatchthemsay, "Me?

Ilost.""Me?

Ilost." Now,ifyouwatchnine-and-a-halfyearsoftelevision-- nosleep,nopottybreaks--andyousawlossafterlossafterloss,andthenattheendthere's30secondsof,"andIwon," thelikelihoodthatyouwouldplaythelotteryisverysmall.

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17Look,Icanprovethistoyou:

here'salittlelottery. There's10ticketsinthislottery. Nineofthemhavebeensoldtotheseindividuals. Itcostsyouadollartobuytheticketand,ifyouwin, youget20bucks.Isthisagoodbet?

 Well,Bernoullitellsusitis. Theexpectedvalueofthislotteryistwodollars; thisisalotteryinwhichyoushouldinvestyourmoney. Andmostpeoplesay,"OK,I'llplay."

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39Now,aslightlydifferentversionofthislottery:

 imaginethatthenineticketsareallowned byonefatguynamedLeroy. Leroyhasninetickets;there'soneleft. Doyouwantit?

Mostpeoplewon'tplaythislottery.Now,youcanseetheoddsofwinninghaven'tchanged, butit'snowfantasticallyeasytoimaginewho'sgoingtowin. It'seasytoseeLeroygettingthecheck,right?

 Youcan'tsaytoyourself,"I'maslikelytowinasanybody," becauseyou'renotaslikelytowinasLeroy. Thefactthatallthoseticketsareownedbyoneguy changesyourdecisiontoplay, eventhoughitdoesnothingwhatsoevertotheodds.

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13Now,estimatingodds,asdifficultasitmayseem,isapieceofcake comparedtotryingtoestimatevalue:

 tryingtosaywhatsomethingisworth,howmuchwe'llenjoyit, howmuchpleasureitwillgiveus. Iwanttotalknowabouterrorsinvalue. HowmuchisthisBigMacworth?

Isitworth25dollars?

 Mostofyouhavetheintuitionthatit'snot-- youwouldn'tpaythatforit.

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37Butinfact,todecidewhetheraBigMacisworth25dollarsrequires thatyouaskone,andonlyonequestion,whichis:

 WhatelsecanIdowith25dollars?

 Ifyou'veevergottenononeofthoselong-haulflightstoAustralia andrealizedthatthey'renotgoingtoserveyouanyfood, butsomebodyintherowinfrontofyouhasjustopened theMcDonald'sbag,andthesmellofgoldenarches iswaftingovertheseat,youthink, Ican'tdoanythingelsewiththis25dollarsfor16hours. Ican'tevensetitonfire--theytookmycigarettelighter!

 Suddenly,25dollarsforaBigMacmightbeagooddeal.

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10Ontheotherhand,ifyou'revisitinganunderdevelopedcountry, and25dollarsbuysyouagourmetmeal,it'sexorbitantforaBigMac. Whywereyouallsurethattheanswertothequestionwasno, beforeI'deventoldyouanythingaboutthecontext?

 BecausemostofyoucomparedthepriceofthisBigMac tothepriceyou'reusedtopaying.Ratherthanasking, "WhatelsecanIdowithmymoney,"comparingthisinvestment tootherpossibleinvestments,youcomparedtothepast. Andthisis