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Hack 33. Predict the Length of a Lifetime

# Hack 33. Predict the Length of a Lifetime

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privilegedplaceintheuniverse.

It'simportanttochoosesubjectsatordinary,unprivileged

moments.Biasingyourtestbychoosingsubjectsthatyou

spansuchasthehumanoccupantsofaneonatalwardora

Plentyofactuarialdataisavailableonthehumanlifespan

Havingchosenamoment,let'sexamineit.Allelsebeingequal,

there'sa50percentchancethemomentissomewhereinthe

chanceit'sinthemiddle60percent,a95percentchanceit'sin

themiddle95percent,andsoon.Therefore,there'sonlya25

percentchancethatyou'vechosenamomentinthefirstfourth

percentchanceit'sinthelast2.5percentofthesubject's

Table3-11providesequationsforthe50percent,60percent,

and95percentconfidencelevels.Thevariabletpastrepresents

howlongtheobjecthasexisted,andtfuturerepresentshow

longitisexpectedtocontinue.

TableConfidencelevelsunderGott'sPrinciple

Confidencelevel

Minimumtfuture

Maximumtfuture

60percent

tpast/3

tpast/4

3tpast

4tpast

95percent

tpast/39

39tpast

50percent

Let'slookatasimpleexample.Quick:whoseworkdoyouthink

ismorelikelytobelistenedto50yearsfromnow,Johann

SebastianBach'sorBritneySpears'?Bach'sfirstworkwas

performedaround1705.Atthetimeofthiswriting,that's300

yearsago.BritneySpears'firstalbumwasreleasedinJanuary

ConsultingTable3-11,forthe60percentconfidencelevel,we

seethattheminimumtfutureistpast/4,andthemaximumis

4tpast.SincetpastforBritney'smusicis79months,thereisa

60percentchancethatBritney'smusicwillbeheardfor

between79/4monthsand79x4monthslonger.Inotherwords,

wecanbe60percentsurethatBritneywillbeaculturalforce

forsomewherebetween19.75months(1.6years)and316

months(26.3years)fromnow.

Sixtypercentisagoodconfidencelevelforquickestimation;notonlyis

itabetter-than-evenchance,butthefactors1/4and4areeasytouse.

Bythesametoken,wecanexpectpeopletolistentoBach's

musicforsomewherebetweenanother300/4and300x4years

atthe60percentconfidencelevel,orsomewherebetween75

yearsand1,200yearsfromnow.Thus,wecanpredictthat

there'sagoodchancethatBritney'smusicwilldiewithher

fans,andthere'sagoodchancethatBachwillbelistenedtoin

thefourthmillennium.

HowItWorks

chancewearesomewhereinthemiddle60percentofthe

Ifweareattheveryendofthismiddle60percent,weareat

thesecondpointmarked"now?"inFigure3-4.Atthispoint,

the60percentconfidencelevel.

percentconfidencelevel)

Similarly,ifweareatthebeginningofthemiddle60percent

(thefirstpointmarked"now?"inFigure3-4),80percentofthe

target'sexistenceliesinthefuture,asdepictedinFigure3-6.

Therefore,tfuture(80percent)isequalto4xtpast(20percent).

currentconfidencelevel.

percentconfidencelevel)

Sincethere'sa60percentchancewe'rebetweenthesetwo

points,wecancalculatewith60percentconfidencethatthe

futuredurationofthetarget(tfuture)isbetweentpast/4and

4xtpast.

InRealLife

Supposeyouwanttoinvestinacompanyandyouwantto

estimatehowlongthecompanywillbearoundtodetermine

whetherit'sagoodinvestment.YoucanuseGott'sPrincipleto

thepublisherofthisbook,asanexample.

Icertainlydidn'tpickO'ReillyMediaatrandom,andplentyofhistorical

longevityanyway.Afterall,there'sprobablygooddataonthelongevity

hesitatetosaythatnowthatO'ReillyhaspublishedMindPerformance

Hacks,itsimmortalityisassured.

AccordingtotheWikipedia,O'Reillystartedin1978asa

consultingfirmdoingtechnicalwriting.It'sJuly2005asIwrite

this,soO'Reillyhasexistedasacompanyforapproximately27

years.HowlongcanweexpectO'Reillytocontinuetoexist?

confidencelevel:

Minimum

27/3=9years(untilJuly2014)

Maximum

27x3=81years(untilJuly2086)

Hereareourexpectationsatthe60percentconfidencelevel:

Minimum

27/4=6yearsand9months(untilApril2012)

Maximum

27x4=108years(untilJuly2113)

Finally,here'sourpredictionwith95percentconfidence:

Minimum

mid-March2006)

Maximum

27x39=1,053years(untilJuly3058)

Inthepost-dot-comeconomy,thesefigureslookprettygood.

Forexample,AppleComputer'saren'tmuchbetter,and

Microsoftwasfoundedin1975,sothesamecanbesaidforit.A

realinvestorwouldwanttoconsidermanyotherfactors,such

asannualrevenueandstockprice,butasafirstcut,itlooksas

thoughO'ReillyMediaisatleastaslikelytooutlivea

Endnotes

1. Ferris,Timothy."HowtoPredictEverything."TheNew

Yorker,July12,1999.

2. Gott,J.RichardIII."ImplicationsoftheCopernican

PrincipleforOurFutureProspects."Nature,363,May27,

1993.

3. Gott,J.RichardIII."AGrimReckoning."

http://pthbb.org/manual/services/grim.

RonHale-Evans

Hack34.MakeWiseMedicalDecisions

Medicaltestsprovidediagnosticscreeninginformation

thatisoftenmisunderstoodbypatientsand,sometimes,

evenbydoctors.Understandingtheprobability

characteristicscalled"sensitivity"and"specificity"can

provideamoreaccurateand(sometimes)reassuring

picture.

Asaconsumerofmedicalinformation,youhavetomake

andsoon.Youlikelyrelyonmedicalinformationnewspaper

decisions.However,muchofthemedicalinformationyouget

fromyourdoctorhasaknownamountoferror.Thisisespecially

thatyouhaveacertaincondition.

ofthosemedicalteststogetamoreaccuratepictureofreality

StatisticsandMedicalScreening

Tousemedicaltestinformationwisely,wehavetolearnjusta

Thefourpossibleoutcomesofmedicaltests,intermsof

accuracy,areshowninTable3-12.

TablePossiblemedicaltestoutcomes

Patientactuallyhas Patientactuallydoes

nothavecondition(B)

thecondition(A)

Testresultindicatespatient

hascondition

Testresultindicatespatient

doesnothavecondition

Truepositive(scoreis

correct)

Falsenegative(scoreis

wrong)

Falsepositive(scoreis

wrong)

Truenegative(scoreis

correct)

Thereliability[Hack#6]ofmedicalscreeningtestsis

summarizedbytwoproportionscalledsensitivityandspecificity.

Essentially,thosewhorelyonthesetestsareconcernedwith

threequestionsofaccuracy:

Ifapersonhasthedisease,howlikelyisthepersonto

scoreapositivetestresult?Thislikelihoodissensitivity.Of

positivetestresult?

Ifthepersondoesnothavethedisease,howlikelyisthe

persontoscoreanegativetestresult?Thislikelihoodis

specificity.OfthosepeopleincolumnB,whatpercentwill

Ifapersonscoresapositivetestresult,howlikelyisthe

persontohavethedisease?Fromthepatient'sperspective,

thisistheultimatequestion,anditcanbethoughtofasthe

basicvalidityconcernwiththesetests.Doctor,canItrust

thesetestresults,orcouldtherebesomemistake?

NoticeinTable3-12thattherearedifferentpeopleincolumnsAandB.

PeoplewiththediseaseareincolumnAandpeoplewithoutthedisease

areincolumnB.IfyouareincolumnA,youcannotscoreafalse

positiveonthetest,becauseapositiveresultiscorrect.Ifyouarein

columnB,youcannotscoreafalsenegative,becauseanegativeresult

iscorrect.

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Hack 33. Predict the Length of a Lifetime

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