Or RR Pressentation

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1/13

Relative Risk, Odds Ratio and

Attributable Risk


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22

Measuring Disease FrequencyMeasuring Disease Frequency

DiseaseDisease Yes Yes

DiseaseDiseaseNoNo

TOTALTOTAL

ExposeExposedd

Yes Yes

AA BB A+BA+B

ExposeExpose

dd

NoNo

CC DD C+DC+D

TOTALTOTAL A+CA+C B+DB+D A+C+DA+C+D

In any study one o! t"e #rst steps is to gat"er data$In any study one o! t"e #rst steps is to gat"er data$

T"e c"art a%o&e is ca''ed aT"e c"art a%o&e is ca''ed a C"i (quareC"i (quare and it is t"e and it is t"e%asic statistic used to test !or t"e signi#cance o! any%asic statistic used to test !or t"e signi#cance o! anydi)erences noted in distri%ution o! disease or ris*$di)erences noted in distri%ution o! disease or ris*$

ates needed !or epide,io'ogica' ana'ysis can %eates needed !or epide,io'ogica' ana'ysis can %e

ca'cu'ated !ro, t"is %asic ta%'e$ca'cu'ated !ro, t"is %asic ta%'e$


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C"iC"i(quare(quare

DiseaseDisease

Yes Yes

DiseaseDisease

NoNo

TOTALTOTAL

ExposedExposed

Yes Yes

AA BB A+BA+B

ExposedExposed

NoNo

CC DD C+DC+D

TOTALTOTAL A+CA+C B+DB+D A+C+DA+C+D

A - t"e . /"o are exposed and "a&e t"e disease

B-t"e nu,%er /"o are exposed and do not "a&e t"e disease

C-t"e nu,%er /"o are not exposed and "a&e t"e diseaseD-t"e nu,%er o! indi&idua's /"o are not exposed and don0t "a&e t"edisease

A+B+C+D- t"e tota' nu,%er in t"e popu'ation %eing studied

A+B-t"e tota' nu,%er exposed

C+D-t"e tota' nu,%er not exposed

A-C-t"e tota' nu,%er /it" disease

B+D-t"e tota' nu,%er /it"out disease


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Measuring Disease FrequencyMeasuring Disease Frequency

In epide,io'ogy occurrence o! a condition ,ustIn epide,io'ogy occurrence o! a condition ,ust

%e re'ated to t"e 1popu'ation at ris*2$ Co,,on%e re'ated to t"e 1popu'ation at ris*2$ Co,,on

,easures o! disease !requency are 3re&a'ence,easures o! disease !requency are 3re&a'ence

rate and Incidence rate$rate and Incidence rate$

3re&a'ence rate3re&a'ence rate - t"e proportion o! a- t"e proportion o! a

popu'ation t"at are cases at a point inpopu'ation t"at are cases at a point inti,e$ti,e$

For exa,p'e /"atFor exa,p'e /"at

3O3OTION3O3OTION

O! t"e t"e 4$($ popu'ationO! t"e t"e 4$($ popu'ation

5as 5I67AID( rig"t no/85as 5I67AID( rig"t no/8

For current 5I67AID( statistics c"ec* t"e 'in* %e'o/9For current 5I67AID( statistics c"ec* t"e 'in* %e'o/9

Lin*9Lin*9 CDC : Di&ision o! 5I67AID( 3re&ention : Basic (tatisticsCDC : Di&ision o! 5I67AID( 3re&ention : Basic (tatistics

Source: LC,/1985,David LanceGoines.

http://www.cdc.gov/hiv/stats.htmhttp://www.cdc.gov/hiv/stats.htmhttp://www.cdc.gov/hiv/stats.htmhttp://www.cdc.gov/hiv/stats.htm


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3re&a'ence3re&a'ence ateate

3re&a'ence ate3re&a'ence ate9 t"e proportion o! peop'e in a popu'ation9 t"e proportion o! peop'e in a popu'ation

/"o "a&e a condition7attri%ute at a speci#ed ti,e$/"o "a&e a condition7attri%ute at a speci#ed ti,e$

3re&a'ence3re&a'ence-nu,%er o! existing cases di&ided %y tota'-nu,%er o! existing cases di&ided %y tota'

popu'ationpopu'ation

For exa,p'e a "ypot"etica' sur&ey o! ;?@ /ere "ea&y s,o*ers$ T"e pre&a'encepre&a'ence o!o!

t"e condition "ea&y s,o*ing /ast"e condition "ea&y s,o*ing /as t"e nu,%er o! peop'et"e nu,%er o! peop'e

/"o s,o*e "ea&i'y at a speci#ed ti,e di&ided %y t"e tota'/"o s,o*e "ea&i'y at a speci#ed ti,e di&ided %y t"e tota'

popu'ationpopu'ation

>?@ x ?@@ - ?;$>?@ x ?@@ - ?;$

;


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Incidence ateIncidence ate - rate at /"ic" NE cases- rate at /"ic" NE casesoccur in a popu'ation during a speci#ed ti,e period$occur in a popu'ation during a speci#ed ti,e period$

For exa,p'e /"at is t"eFor exa,p'e /"at is t"e

Incidence ateIncidence ate !or!or

ne/ cases o! AID(ne/ cases o! AID(

in a countryin a country

during t"e 'ast year8during t"e 'ast year8

For current 5I67AID( statistics c"ec* t"e 'in* %e'o/9For current 5I67AID( statistics c"ec* t"e 'in* %e'o/9

Lin*9Lin*9 CDC : Di&ision o! 5I67AID( 3re&ention : Basic (tatisticsCDC : Di&ision o! 5I67AID( 3re&ention : Basic (tatistics

Source: LC,/1985,David LanceGoines.

http://www.cdc.gov/hiv/stats.htmhttp://www.cdc.gov/hiv/stats.htmhttp://www.cdc.gov/hiv/stats.htm


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Incidence RateIncidence Rate

rate at which N! cases occur in a "o"u#ation durin$ a s"eci%edrate at which N! cases occur in a "o"u#ation durin$ a s"eci%ed

ti&e "eriod. 'or e(a&"#e, in a h)"othetica# stud) o* +9- co##e$eti&e "eriod. 'or e(a&"#e, in a h)"othetica# stud) o* +9- co##e$ewo&en, 8+ dran two or &ore $#asses o* a#coho# a da). 0went)wo&en, 8+ dran two or &ore $#asses o* a#coho# a da). 0went)

seven o* the 8+ twoada) wo&en driners over a s"eci%ed ti&eseven o* the 8+ twoada) wo&en driners over a s"eci%ed ti&e

"eriod were in car accidents re#ated to a#coho# use. 0he"eriod were in car accidents re#ated to a#coho# use. 0he incidencerate o* a#coho#re#ated car accidents was:o* a#coho#re#ated car accidents was:

2#coho#re#ated car accidents2#coho#re#ated car accidents

divided 3) twoada) driners.divided 3) twoada) driners.

+4+4

8+ 1-- 6 5.78+ 1-- 6 5.7

!arten3er$, Danie#. +---. 2na#)tica#;ethods


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Measures 4sed to ("o/ (tatistica'Measures 4sed to ("o/ (tatistica'

Corre'ation9Corre'ation9

= Is t"is disease increasing in incidence8Is t"is disease increasing in incidence8

= Is it ,ore !requent in ,y area8Is it ,ore !requent in ,y area8

= Does its incidence corre'ate /it"Does its incidence corre'ate /it"

so,e suspected cause8so,e suspected cause8

= 5a&e t"ings c"anged since /e5a&e t"ings c"anged since /e

introduced contro' ,easures8introduced contro' ,easures8

T"ese are a'' questions /e ans/er %y setting t/oT"ese are a'' questions /e ans/er %y setting t/o

sets o! rates side %y side and co,paring t"e,$sets o! rates side %y side and co,paring t"e,$

T"ree co,,on ,easures /e use to co,pare ratesT"ree co,,on ,easures /e use to co,pare rates

areare

e'ati&e is* Odds atio ande'ati&e is* Odds atio and

Source>LC/?ero&e @enr) Rothstein,1978

'or in*or&ation on cancer and the #in to'or in*or&ation on cancer and the #in to

nutrition $o to:nutrition $o to:

"i Research: Nutritiona# "ide&io#o$)"i Research: Nutritiona# "ide&io#o$)

http://www.epi.umn.edu/epi_pages/research/nutrition.htmlhttp://www.epi.umn.edu/epi_pages/research/nutrition.htmlhttp://www.epi.umn.edu/epi_pages/research/nutrition.htmlhttp://www.epi.umn.edu/epi_pages/research/nutrition.htmlhttp://www.epi.umn.edu/epi_pages/research/nutrition.html


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e'ati&e is* e'ati&e is*

= Ca'cu'ated to identi!y di)erences in disease ratesCa'cu'ated to identi!y di)erences in disease rates

%et/een exposed and unexposed groups$ It is t"e%et/een exposed and unexposed groups$ It is t"e,ost co,,on ,easure o! association used %y,ost co,,on ,easure o! association used %y

epide,io'ogists %ecause it can %e esti,ated %y aepide,io'ogists %ecause it can %e esti,ated %y a

/ider range o! study designs$/ider range o! study designs$

= e'ati&e is* e'ati&e is* - ate o! condition a,ong exposed- ate o! condition a,ong exposeddi&ided %y rate o! condition a,ong unexposeddi&ided %y rate o! condition a,ong unexposed

For exa,p'e i! 'ung cancer ,orta'ity rate a,ongFor exa,p'e i! 'ung cancer ,orta'ity rate a,ong

s,o*ers is ?>? per ?@@@@@ and t"e 'ung cancer rates,o*ers is ?>? per ?@@@@@ and t"e 'ung cancer rate

a,ong non:s,o*ers is ?? per ?@@@@@ t"ena,ong non:s,o*ers is ?? per ?@@@@@ t"en

e'ati&e is* e'ati&e is* - ?>?7??-??$- ?>?7??-??$

e'ati&e is* - ? ,eans no di)erencee'ati&e is* - ? ,eans no di)erence

e'ati&e is* ? s"o/s existence o! ane'ati&e is* ? s"o/s existence o! an

association %et/een exposure and diseaseassociation %et/een exposure and disease

and t"ere is an association %et/eenand t"ere is an association %et/een

s,o*ing and 'ung cancer$s,o*ing and 'ung cancer$


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11

00

Odds atioOdds atio

= Ca'cu'ated to identi!y 'i*e'i"ood o! exposure to ris*Ca'cu'ated to identi!y 'i*e'i"ood o! exposure to ris*

/"en co,paring t/o groups one /it" and one/"en co,paring t/o groups one /it" and one/it"out disease$/it"out disease$

= Odds atioOdds atio - Exposure odds in disease group- Exposure odds in disease groupdi&ided %y exposure odds in non:disease groupdi&ided %y exposure odds in non:disease group

I! t"e pre&a'ence o! s,o*ing a,ong 'ung cancerI! t"e pre&a'ence o! s,o*ing a,ong 'ung cancer

patients is per ?@@ and t"e pre&a'ence o! s,o*ingpatients is per ?@@ and t"e pre&a'ence o! s,o*ing

a,ong peop'e /it"out 'ung cancer is ; per ?@@ t"ena,ong peop'e /it"out 'ung cancer is ; per ?@@ t"en

Odds atioOdds atio - 7;->$- 7;->$

atio - ? no associationatio - ? no associationatio ? association %et/eenatio ? association %et/een

exposure and diseaseexposure and disease

G G$$And t"ere is an association$$And t"ere is an association

%et/een 'ung cancer and s,o*ing$%et/een 'ung cancer and s,o*ing$ead a%out so,e interesting studies on yout" and s,o*ing


11/13

11

11

DiseaseDisease

(tatus(tatus

. o! s,o*ers. o! s,o*ers . o!. o!

nons,o*ernons,o*erss

3:&a'ue3:&a'ue

Ma'es

Lung cancer

HJ

Ma'es

Contro's

H;;

$J

;=


12/13

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22

2ttri3uta3#e Ris2ttri3uta3#e Ris

2ttri3uta3#e Ris2ttri3uta3#e Ris is the "ro"ortion o* e("osed casesis the "ro"ortion o* e("osed cases

that wou#d not have $otten the disease i* the) had notthat wou#d not have $otten the disease i* the) had not3een e("osed.3een e("osed.

'or e(a&"#e: @ow &an)'or e(a&"#e: @ow &an)

;AR "eo"#e wi## $et cancer;AR "eo"#e wi## $et cancer

in a town that has arsenicin a town that has arsenic

conta&ination due to industria#conta&ination due to industria#

"o##utionB"o##utionB 0he 2ttri3uta3#e Ris wou#d 3e use*u# to now in this case, 0he 2ttri3uta3#e Ris wou#d 3e use*u# to now in this case,

3ecause we &a) then 3e a3#e to attri3ute this e(cess o*3ecause we &a) then 3e a3#e to attri3ute this e(cess o*disease to the ris *actor were stud)in$.disease to the ris *actor were stud)in$.


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2ttri3uta3#e Ris2ttri3uta3#e Ris

I* we su3tract the rate o* disease in a "o"u#ation that doesI* we su3tract the rate o* disease in a "o"u#ation that does

not have a ris *actor *ro& the rate o* disease in anot have a ris *actor *ro& the rate o* disease in a

"o"u#ation that DAS have a ris *actor, we $et the"o"u#ation that DAS have a ris *actor, we $et the

2ttri3uta3#e Ris.2ttri3uta3#e Ris.

Rate o* Disease/ e("osed

&inus

Rate o* Disease/ not e("osed

6 2ttri3uta3#e Ris.

'or e(a&"#e: Lets sa) that in a town e("osed to arsenic *ro& "o##ution, we %nd ten cases o* one

t)"e o* cancer in +--- "eo"#e over a 1-)ear "eriod o* o3servation. 0he rate, then, is cases "er1-,--- "eo"#e "er )ear. Co&"arin$ the rate in this town to that esti&ated *or the entire

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