Tutorial Tambahan Tiara 3 Nov 2011

7/29/2019 Tutorial Tambahan Tiara 3 Nov 2011

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Kelas MKO KMPK

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Casecontrol:

Case Ca paru R

on ro e as a paruIntervention Control

penyakitnya

em an ng an proporspaparan (merokok vs tidakmerokok)

u come u come

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Seluruh populasi, Cohort study

paparannya. Population

Yangdibandingkan:Non Random Allocation

Angka kejadian

en akitn aGroup A Group B

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Lebih mudah menemukan kasus diRS

Akses ke rekam medis yanglengkap

as en cen erung e mu a a a e er asama(karena penelitian ini tentang penyakit yang

Mudah mendapatkan kontrol

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Akta kematian,laboratorium patologi klinik,

data

, ,

kerja

Tetangga,teman,pasien laindari dokter yang

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Kemungkinan besar berasal dari lingkungan

ekonomi,

tempat tinggal,

akses ke layanan,

Rekam medis standard

Mudah bekerjasama

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dirawat karena penyakit lainyangjuga

disebabkan oleh merokok

Sehingga,kebiasaan merokok pada kontrolakan lebih tin i dari ada o ulasi normal

hubungan antara merokok dan Ca Paruakan ?

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Cases Controls

Cigare e smoker 1,350 1,296

Non-smoker 7 61

T a ,357 ,357

Proporsi perokok pada kasus: 1.350/1.357=99.5%

Proporsi perokok pada kontrol: 1.296/1.357=95.5%

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Oddsmerokok pada pasien Ca Paru (kasus):

Odds = probability / (1 - probability) = proportion / (1 - proportion)

Odds of smoking, cases:= = . :

Odds = #yes / #no = #wins / #losses = #exposed / #unexposed

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12 1 1 1 =12 1 =21.2 : 1

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Ra io of odds = (a/c) (b d) =(1350 7) (1296 61) =192.9 21.2 =9.1

C oss- oduc a io =(a d b c) =(1350 61) (12 6 7) = .

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Jumlah rokok #kasus #Kontrol

114

rokok/hari 565 706

=

7/61

1-14 ciga e es, OR =(565 61) / (706 7) = 7.0

15-24 ciga e es, OR = 445 61 408 7 = 9.525+ cigarettes, OR = (340 x 61) / (182 x 7 ) =16.3

All smokers, OR = (1350 x 61) / (1296 x 7) = 9.1

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Selectionbias

In ormation ias

Confounding Investigatorerror

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Daily Rate

number of Deaths Person- Mortality rate differencecigarettes from lung years per 1000 Rate per 1000smo ed cancer a ris erson- ears Ratio erson- ears

0 3 42,800 0.07 referent referent

1-14 22 38,600 0.57 8.1 0.50

15-24 54 38,900 1.39 19.8 1.32

25+ 57 25,100 2.27 32.4 2.20

All smokers 133 102,600 1.30 18.6 1.23

Total 136 145,400 0.94

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The twomajortypesofbias:

Measurement bias

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characteristicsof

people

selected for

astudy

and

those notselected

If it occurs: we see a relation between risk factor and disease

that is different in those in the study compared

not participate

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Whyisitimportant?

resultsto

THE

WHOLE

POPULATION

eg Letstryandfindoutwhatproportionofpost

menopausalwomen

in

Australia

use

HRT?

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Remember..

Wheneverwedoastud weselecta rou of

people,

do

the

study,

get

the

result...

Wethenusetheresulttogeneralizetothewhole

population

eg isthisthetrueprevalenceofwomenonHRTin

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Prevalenceofpostmenopausalwomenin

Australia

usin

HRT?

AskALL

women

GotoGP

Recruitfromgyms

Randomtelephonecontact

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have effected the type of subjects you have in yourstudy

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=

Advertisein

the

newspapers

=?

health

conscious

women

GotoGP=?morelikelytobeonHRT Recruitfromshoppingcentres=?healthconsciouswomen Recruitfromgyms=?healthconsciouswomen =

home

Randomtelephonecontact=?lesshealthconsciouswomen

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Selectionbiasincasecontrolstudies

an e a ma or pro em

Controlsshouldbeselectedsothattheyrepresent

drawn.

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Selectionbiasincasecontrolstudies

Eg Case control study of childhood brain tumor. Cases

.

How do we find controls? How might you do this?

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Hospitalbasedcontrols Oftenused

Couldtherebeaproblem?

Best=matched

to

post

code.

Why?

E Casecontrolstud oflun cancerattheAlfredHospital.Canyoucollectcontrolsfromthe

orthopoedic unit?

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Less problem because exposure is identified,

group selected

eg potential problem if general population is used

healthy worker effect

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Thosethat

drop

out

of

the

study

NOT

the

same

as

thosethatsta inastud

Mayintroducebias

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Occurswhen

the

measurement

or

classification

of

diseaseorriskfactorare notaccurate

supposedtomeasure

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:

server o server as

Studyparticipant

(responder

bias)

Theinstruments e.g.questionnaireorsphygmomanometer)usedtomakethe

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Tutorial Tambahan Tiara 3 Nov 2011