Or RR Pressentation 04 April 2014
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Transcript of Or RR Pressentation 04 April 2014
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Relative Risk, Odds Ratio
and Attributable Risk
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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.
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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
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#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,$avid 3ance:oines.
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(revalence(revalence RateRate
(revalence Rate(revalence Rate2 the proportion of people in a population2 the proportion of people in a population
+ho have a condition0attribute at a specied ti"e.+ho have a condition0attribute at a specied ti"e.
(revalence(revalence)nu"ber of e*isting cases divided by total)nu"ber of e*isting cases divided by total
populationpopulation
%or e*a"ple, a hypothetical survey of ;<== persons sho+ed%or e*a"ple, a hypothetical survey of ;<== persons sho+ed
that >6? +ere heavy s"okers. Thethat >6? +ere heavy s"okers. The prevalenceprevalence of theof thecondition, heavy s"oking, +as the nu"ber of people +hocondition, heavy s"oking, +as the nu"ber of people +ho
s"oke heavily at a specied ti"e divided by the totals"oke heavily at a specied ti"e divided by the total
populationpopulation
>6? * 6?? ) 6;.9@>6? * 6?? ) 6;.9@
;<==;<==
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Incidence RateIncidence Rate ) rate at +hich B cases occur in a) rate at +hich B cases occur in a
population during a specied ti"e period.population during a specied ti"e period.
%or e*a"ple, +hat is the%or e*a"ple, +hat is the
Incidence RateIncidence Rate forfor
ne+ cases of AI$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.
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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 ;=, ;??;
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#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
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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.
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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 $rug Abuse 4 Research %indings 90?6
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DiseaseDisease
S!a!usS!a!us
" o' s%o*ers" o' s%o*ers " o'" o'
nons%o*ernons%o*erss
,$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
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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.
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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: