Or RR Pressentation 04 April 2014

7/17/2019 Or RR Pressentation 04 April 2014

http://slidepdf.com/reader/full/or-rr-pressentation-04-april-2014 1/13

Relative Risk, Odds Ratio

and Attributable Risk



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 of the rst steps is to gather data. The chartabove is called a Chi Suare, and it is the basic statistic

used to test for the signicance of any di!erences noted indistribution of disease or risk.

Rates needed for epide"iological analysis can be calculated

fro" this basic table.



33

ChiChiSquareSquare

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+B+C+DA+B+C+D

A !he " #ho are exposed and ha$e !he disease

B!he nu%&er #ho are exposed and do no! ha$e !he disease

C!he nu%&er #ho are no! exposed and ha$e !he disease

D!he nu%&er o' indi$idua(s #ho are no! exposed and don)! ha$e !hedisease

A+B+C+D !he !o!a( nu%&er in !he popu(a!ion &eing s!udied

A+B!he !o!a( nu%&er exposed

C+D!he !o!a( nu%&er no! exposed

AC!he !o!a( nu%&er #i!h disease



4 4

#easuring $isease %reuency#easuring $isease %reuency

In epide"iology, occurrence of a condition "ust beIn epide"iology, occurrence of a condition "ust be

related to the &population at risk'. Co""on "easuresrelated to the &population at risk'. Co""on "easures

of disease freuency are (revalence rate and Incidenceof disease freuency are (revalence rate and Incidence

rate.rate.

(revalence rate(revalence rate ) the proportion of a) the proportion of a

population that are cases at a point in ti"e.population that are cases at a point in ti"e.

%or e*a"ple, +hat%or e*a"ple, +hat

(RO(ORTIO(RO(ORTIO

Of the the -.S. populationOf the the -.S. population

as I/0AI$S right no+1as I/0AI$S right no+1

%or current I/0AI$S statistics, check the link belo+2%or current I/0AI$S statistics, check the link belo+2

3ink23ink2 C$C 4 $ivision of I/0AI$S (revention 4 5asic StatisticsC$C 4 $ivision of I/0AI$S (revention 4 5asic Statistics

Source2 3C,06789,$avid 3ance:oines.

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






55

(revalence(revalence RateRate

(revalence Rate(revalence Rate2 the proportion of people in a population2 the proportion of people in a population

+ho have a condition0attribute at a specied ti"e.+ho have a condition0attribute at a specied ti"e.

(revalence(revalence)nu"ber of e*isting cases divided by total)nu"ber of e*isting cases divided by total

populationpopulation

%or e*a"ple, a hypothetical survey of ;<== persons sho+ed%or e*a"ple, a hypothetical survey of ;<== persons sho+ed

that >6? +ere heavy s"okers. Thethat >6? +ere heavy s"okers. The prevalenceprevalence of theof thecondition, heavy s"oking, +as the nu"ber of people +hocondition, heavy s"oking, +as the nu"ber of people +ho

s"oke heavily at a specied ti"e divided by the totals"oke heavily at a specied ti"e divided by the total

populationpopulation

>6? * 6?? ) 6;.9@>6? * 6?? ) 6;.9@

;<==;<==



66

Incidence RateIncidence Rate ) rate at +hich B cases occur in a) rate at +hich B cases occur in a

population during a specied ti"e period.population during a specied ti"e period.

%or e*a"ple, +hat is the%or e*a"ple, +hat is the

Incidence RateIncidence Rate forfor

ne+ cases of AI$Sne+ cases of AI$S

in a countryin a country

during the last year1during the last year1

%or current I/0AI$S statistics, check the link belo+2%or current I/0AI$S statistics, check the link belo+2

3ink23ink2 C$C 4 $ivision of I/0AI$S (revention 4 5asic StatisticsC$C 4 $ivision of I/0AI$S (revention 4 5asic Statistics

Source2 3C,06789,$avid 3ance:oines.






77

Incidence RateIncidence Rate

rate at +hich B cases occur in a population during arate at +hich B cases occur in a population during a

specied ti"e period. %or e*a"ple, in a hypotheticalspecied ti"e period. %or e*a"ple, in a hypothetical

study of ;>7? college +o"en, <8; drank t+o or "orestudy of ;>7? college +o"en, <8; drank t+o or "ore

glasses of alcohol a day. T+enty4seven of the <8; t+o4glasses of alcohol a day. T+enty4seven of the <8; t+o4

a4day +o"en drinkers over a specied ti"e perioda4day +o"en drinkers over a specied ti"e period

+ere in car accidents related to alcohol use. The+ere in car accidents related to alcohol use. Theincidence rate of alcohol4related car accidents +as2of alcohol4related car accidents +as2

Alcohol4related car accidentsAlcohol4related car accidents

divided by t+o4a4day drinkers.divided by t+o4a4day drinkers.

;=;=

<8; 6?? ) 9.D@<8; 6?? ) 9.D@

Bartenberg, $aniel. E;???F. Analytical#ethods -sed by pide"iologists..

%ACST Reporting Tools2 online,Septe"ber ;=, ;??;



88

#easures -sed to Sho+ Statistical Correlation2#easures -sed to Sho+ Statistical Correlation2

G

Is this disease increasing in incidence1Is this disease increasing in incidence1G Is it "ore freuent in "y area1Is it "ore freuent in "y area1

G $oes its incidence correlate +ith$oes its incidence correlate +ith

so"e suspected cause1so"e suspected cause1

G ave things changed since +eave things changed since +e

introduced control "easures1introduced control "easures1

These are all uestions +e ans+er by setting t+o sets of These are all uestions +e ans+er by setting t+o sets ofrates side by side and co"paring the". Three co""onrates side by side and co"paring the". Three co""on

"easures +e use to co"pare rates are"easures +e use to co"pare rates are

Relative Risk, Odds Ratio, and Attributable RiskRelative Risk, Odds Ratio, and Attributable Risk

SourceH3C0ero"e enry Rothstein,67>D4>8

%or infor"ation on cancer and the link to%or infor"ation on cancer and the link to

nutrition go to2nutrition go to2

pi Research2 utritional pide"iologypi Research2 utritional pide"iology

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





99

Relative RiskRelative Risk

G Calculated to identify di!erences in disease rates bet+eenCalculated to identify di!erences in disease rates bet+een

e*posed and une*posed groups. It is the "ost co""one*posed and une*posed groups. It is the "ost co""on"easure of association used by epide"iologists, because it"easure of association used by epide"iologists, because it

can be esti"ated by a +ider range of study designs.can be esti"ated by a +ider range of study designs.

G Relative RiskRelative Risk ) Rate of condition a"ong e*posed divided) Rate of condition a"ong e*posed divided

by rate of condition a"ong une*posedby rate of condition a"ong une*posed

%or e*a"ple, if lung cancer "ortality rate a"ong s"okers%or e*a"ple, if lung cancer "ortality rate a"ong s"okersis 6>6 per 6??,???, and the lung cancer rate a"ong non4is 6>6 per 6??,???, and the lung cancer rate a"ong non4

s"okers is 66 per 6??,???, thens"okers is 66 per 6??,???, then

Relative RiskRelative Risk ) 6>6066)66.7) 6>6066)66.7

Relative Risk ) 6 "eans no di!erenceRelative Risk ) 6 "eans no di!erence

Relative Risk J 6 sho+s e*istence of anRelative Risk J 6 sho+s e*istence of an

association bet+een e*posure and disease,association bet+een e*posure and disease,

and there is an association bet+eenand there is an association bet+een

s"oking and lung cancer.s"oking and lung cancer.



11

00

Odds RatioOdds Ratio

G Calculated to identify likelihood of e*posure to risk +henCalculated to identify likelihood of e*posure to risk +hen

co"paring t+o groups, one +ith and one +ithout disease.co"paring t+o groups, one +ith and one +ithout disease.G Odds RatioOdds Ratio ) *posure odds in disease group divided by) *posure odds in disease group divided by

e*posure odds in non4disease groupe*posure odds in non4disease group

If the prevalence of s"oking a"ong lung cancer patients is 79If the prevalence of s"oking a"ong lung cancer patients is 79

per 6??, and the prevalence of s"oking a"ong people +ithoutper 6??, and the prevalence of s"oking a"ong people +ithout

lung cancer is ;9 per 6??, thenlung cancer is ;9 per 6??, then

Odds RatioOdds Ratio ) 790;9)>.8) 790;9)>.8

Ratio ) 6, no associationRatio ) 6, no association

Ratio J 6, association bet+eenRatio J 6, association bet+een

e*posure and diseasee*posure and disease

K K..And there is an association..And there is an association

bet+een lung cancer and s"oking.bet+een lung cancer and s"oking.

Read about so"e interesting studies on youth and s"oking at2

pide"iology of Louth $rug Abuse 4 Research %indings 90?6

http://www.drugabuse.gov/ICAW/epidemiology/epidemiologyfindings501.html

http://www.drugabuse.gov/ICAW/epidemiology/epidemiologyfindings501.html



11

11

DiseaseDisease

S!a!usS!a!us

" o' s%o*ers" o' s%o*ers " o'" o'

nons%o*ernons%o*erss

,$a(ue,$a(ue

Ma(es

Lung cancer

-./

0112/34

5

062734

Ma(es

Con!ro(s

-55

0182934

5/

0.2534

62666666-.

Fe%a(es

Lung cancer

.:

0.-2/34

:1

7:2/34

Fe%a(es

Con!ro(s

59

0.-2/34

75

87273

626:-

S%o*ing and Carcino%a o' !he LungS%o*ing and Carcino%a o' !he Lung

Do(( ;2 Brad'ord< =i(( A2 S%o*ing and carcino%a o' !he (ung> pre(i%inary repor!2

Bri!ish Medica( ?ourna( :186< 5> /71,/.92

Epide%io(ogy o' You!h Drug A&use , ;esearch Findings 8@6:

Based on !he Odds ;a!io 'or%u(a<#ha! is !he Odds ;a!io 'or eachdisease s!a!us in !he 'a%ouss%o*ing s!udy



11

22

Attributable RiskAttributable Risk

Attributable RiskAttributable Risk is the proportion of e*posed casesis the proportion of e*posed cases

that +ould not have gotten the disease if they had notthat +ould not have gotten the disease if they had notbeen e*posed.been e*posed.

%or e*a"ple2 o+ "any%or e*a"ple2 o+ "any

#OR people +ill get cancer#OR people +ill get cancer

in a to+n that has arsenicin a to+n that has arsenic

conta"ination due to industrialconta"ination due to industrial

pollution1pollution1 The Attributable Risk +ould be useful to kno+ in this case, The Attributable Risk +ould be useful to kno+ in this case,

because +e "ay then be able to attribute this e*cess ofbecause +e "ay then be able to attribute this e*cess ofdisease to the risk factor +eMre studying.disease to the risk factor +eMre studying.



1313

Attributable RiskAttributable Risk

If +e subtract the rate of disease in a population that doesIf +e subtract the rate of disease in a population that does

not have a risk factor fro" the rate of disease in anot have a risk factor fro" the rate of disease in a

population that $OS have a risk factor, +e get thepopulation that $OS have a risk factor, +e get the

Attributable Risk.Attributable Risk.

Rate of $isease0 e*posed

"inus

Rate of $isease0 not e*posed

) Attributable Risk.

%or e*a"ple2 3etMs say that in a to+n e*posed to arsenic fro" pollution, +end ten cases of one type of cancer in ;??? people over a 6?4year period ofobservation. The rate, then, is < cases per 6?,??? people per year.Co"paring the rate in this to+n to that esti"ated for the entire -nitedStates, +e nd that this to+n had an e*cess of four cases per 6?,??? peopleper year E9 cases in the to+n "inus one case e*pected based on nationaldata, per 6?,??? persons per year. Be "ay then attribute that e*cess to

arsenic fro" pollution.

Source> LC@:18:

Or RR Pressentation 04 April 2014

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