Sesi 5 b ukuran dampak.2009l

UKURAN DAMPAK

UKURAN ASOSIASI

• Relative : –RR (relative risk)

• Risk ratio• Rate ratio

–OR• Absolute :

–RD (risk difference)

R e l a t i v e r i s kR R O R

A t t r i b u t a b l e r i s kA R P A R

M e a s u r e o fA s s o c i a t i o n

Measures of Public Health ImpactMeasures of Public Health Impact

• Attributable Risk (AR) Number

• Attributable Risk Percent (AR%) Percentage

• Population Attributable Risk (PAR) Number

• Population Attributable Risk Percent

(PAR%) Percentage


IMPORTANT!

They all assume (require) that a cause-effect relationship exists between the exposure and the outcome.

Relative Risk vs. Attributable RiskRelative Risk vs. Attributable Risk

Relative Risk: Measure of the strength of association, and indicator used to assess the possibility of a causal relationship.

Attributable Risk: Measure of the potential for prevention of disease if the exposure could be eliminated (assuming a causal relationship).


Relative Risk:

• Etiology

Attributable Risk:

• Policy decisions

• Funding decisions (e.g. prevention programs)

Tipe ukuran yang digunakan dalam epidemiologi

• Ukuran efek/dampak– Merefleksikan dampak suatu faktor pada

frekuensi atau risiko dari suatu masalah (outcome) kesehatan

– Merefleksikan kelebihan jumlah kasus karena suatu faktor (attributable) atau jumlah kasus yang dapat dicegah oleh eksposur (pemajan)

Ukuran-ukuran dampak

• Ukuran perbedaan dampak/efek– Perbedaan risiko = Risk Difference (RD) =

Attributable Risk (AR) = Excess Risk (ER) = Absolute Risk (AR)

• [Risiko pada kelompok terpajan] – [Risiko pada kelompok tidak terpajan]

• Berguna untuk mengukur besarnya masalah kesehatan masyarakat yang disebabkan oleh suatu pemajan

• bermanfaat untuk penilaian prioritas untuk aksi kesehatan masyarakat (Public Health Action)

Attributable Risk (AR)Attributable Risk (AR)

Among the EXPOSED:

How much of the disease that occurs can be attributed to a certain exposure?

AR

AR%

This is of primary interest to the practicing clinician.


AR = Iexposed – Inonexposed = “Risk Difference”

Smoke Yes No

Yes 84 2916 3000

No 87 4913 5000

Develop CHD ISM = 84 / 3000

= 0.028 = 28.0 / 1000

INS = 87 / 5000

= 0.0174 = 17.4 / 1000

(background risk)

AR = (28.0 – 17.4) / 1000 = 10.6 / 1000


AR = (28.0 – 17.4) / 1000 = 10.6 / 1000

Among SMOKERS, 10.6 of the 28/1000 incident cases of CHD are attributed to the fact that these people smoke …

Among SMOKERS, 10.6 of the 28/1000 incident cases of CHD that occur could be prevented if smoking were eliminated.


• Ukuran perbedaan dampak/efek– Perbedaan insidens kumulatif = Cumulative

Incidence Difference= CID

[IK pada kelompok terpajan] - [IK pada kelompok tidak terpajan]

IK = Insidens Kumulatif


• Ukuran perbedaan efek– Perbedaan rate/ perbedaan densitas insidens

(IDD = Insidence Density Difference)• IDD =

[Densitas insidens dalam kelompok terpajan] - [Densitas insidens pada kelompok tidak terpajan]


• Ukuran perbedaan efek

– Perbedaan prevalens (PD = Prevalence Differrence)

PD = [Prevalens dalam kelompok terpajan] - [Prevalens dalam kelompok tidak terpajan]

Attributable Risk

Incidence

Exposed Unexposed

Iexposed - Iunexposed

Figure 12-1 A, Total risks in exposed and nonexposed groups. B, Background risk. C, Incidence attributable to exposure and

incidence not attributable to exposure.

Downloaded from: StudentConsult (on 8 October 2009 11:44 AM)

© 2005 Elsevier

Figure 12-2 The concept of attributable risk.

Downloaded from: StudentConsult (on 8 October 2009 11:44 AM)

© 2005 Elsevier

AR: Fast driving

Dead Not dead Risk RD

2000 0.05 0.04

8000 0.01

Fast

Slow

100 1900

80 7920

AR: Drunk driving

Dead Not dead Risk RD

Drunk 45 255 300 0.150

Not d. 135 9565 10000 0.014

0.136

Ukuran-ukuran dampak/efek

• Ukuran perbedaan efek– Attributable Risk (AR) Percent = AR%

( ) ( )

( )%100

Insidens

InsidensInsidensAR%

terpajan

terpajantidakterpajan x−

=

Attributable Risk Percent (AR%)Attributable Risk Percent (AR%)

AR% = (Iexposed – Inonexposed) / Iexposed = “Etiologic fraction”

Smoke Yes No

Yes 84 2916 3000

No 87 4913 5000

Develop CHD

AR% = (28.0 – 17.4) / 28.0 = 37.9%

ISM = 84 / 3000

= 0.028 = 28.0 / 1000

INS = 87 / 5000

= 0.0174 = 17.4 / 1000

(background risk)

Attributable Risk Percent (AR%)Attributable Risk Percent (AR%)

AR% = (28.0 – 17.4) / 28.0 = 37.9%

Among SMOKERS, 38% of the morbidity from CHD may be attributed to smoking…

Among SMOKERS, 38% of the morbidity from CHD could be prevented if smoking were eliminated.

Attributable Risk Percent

Incidence

Exposed Unexposed

Iexposed – Iunexposed RR - 1

------------------------------- = ------------ x 100%

Iexposed RR

AR%: Fast driving

Dead Not dead Risk AR%

Fast 100 1900 2000 0.05

Slow 80 7920 8000 0.01

0.05 – 0.01

0.05

= 80%

AR%: Drunk driving

Dead Not dead Risk AR%

Drunk 45 255 300 0.150

Not d. 135 9565 9700 0.014

0.150 – 0.014

150

= 91%

Ukuran-ukuran dampak• Population Attributable Risk (PAR)

– = Attributable Fraction (population) atau Etiologic Fraction (population) = Population Attributable Risk Proportion = Population Attributable Risk Fraction

– Proporsi (atau fraksi) rate penyakit pada seluruh populasi yang mewakili rate penyakit dalam kelompok terpajan

– Rumus PAR

( ) ( )terpajantidakpopulasi InsidensInsidensPAR −=

Population Attributable Risk (PAR)Population Attributable Risk (PAR)

Among the EXPOSED and NONEXPOSED (e.g. total population):

How much of the disease that occurs can be attributed to a certain exposure?

PAR

PAR%

This of interest to policy makers and those responsible for funding prevention programs.

PAR and PAR%PAR and PAR%

Example:

We want to estimate how much of the burden of diabetes among Tampanians is attributed to obesity.

PAR and PAR%PAR and PAR%

CAUTION!

In order to calculate PAR and PAR%, we have to be reasonably sure that the results of the study can be generalized to the population of Tampa.

(e.g the incidence rates drawn from the sample approximate the incidence rates in the entire population).

Population Attributable Risk

Risk

Population Unexposed

unexposed population I -I


PAR = Itotal – Inonexposed

Weight Yes No

Obese 850 3650 4500

Slim 250 5250 5500

Diabetes IT = 1100 / 10000

= 0.11 = 110 / 1000

INE = 250 / 5500

= 0.0455 = 45.5 / 1000

(background risk)

PAR = (110 – 45.5) / 1000 = 64.5 / 1000

1100 8900 10000


PAR = (110 – 45.5) / 1000 = 64.5 / 1000

In Tampa, 64.5 of the 110/1000 incident cases of diabetes are attributed to obesity …

In Tampa, 64.5 of the 110/1000 incident cases of diabetes that occur could be prevented with sufficient weight loss.


• Population Attributable Risk Percent (PARP) attributable fraction (population) atau etiologic fraction (population)– Berarti proporsi kasus baru yang dapat dicegah jika

pada semua orang yang tidak terpajan– Rumus PAR%

( ) ( )

( )%100

Insidens

InsidensInsidensPAR%

populasi

terpajantidakpopulasi x−

=

Population Attributable Risk PercentPopulation Attributable Risk Percent

PAR% = (Itotal – Inonexposed) / Itotal

Weight Yes No

Obese 850 3650 4500

Slim 250 5250 5500

Diabetes

PAR% = (110 – 45.5) / 110 = 58.6%

1100 8900 10000

IT = 1100 / 10000

= 0.11 = 110 / 1000

INE = 250 / 5500

= 0.0455 = 45.5 / 1000

(background risk)

Population Attributable Risk PercentPopulation Attributable Risk Percent

PAR% = (110 – 45.5) / 110 = 58.6%

In Tampa, 59% of the cases of diabetes may be attributed to obesity in the population…

In Tampa, 59% of the cases of diabetes could be prevented if Tampa residents lost sufficient weight.

PAR: Fast driving

Dead Not dead Risk

Fast 100 1900 2000 0.05

Slow 80 7920 8000 0.010

180 9820 10000 0.018

PAR = 0.018 – 0.010 = 0.008

PAR% = (0.018 – 0.014) ; 0.018 x 100% = 44%

PAR: Drunk driving

Dead Not dead Risk

Drunk 45 255 300 0.15

Not drunk 135 9565 9700 0.014

PAR = 0.018 – 0.014 = 0.004

PAR% = (0.018 - 0.014) : 0.018 x 100% = 22%

180 9820 10,000 0.018

Conclude

• 44% of driving-related deaths in population were presumably due to fast driving

• 22% of driving-related deaths in population were presumably due to drunk driving

Summary

Calculating Measures of Calculating Measures of Public Health Impact Public Health Impact

(Case-Control Studies)(Case-Control Studies)

● They are based on measures of incidence.

● We can calculate incidence measures from case-control studies only under special circumstances.

● Therefore, the AR and PAR cannot usually be calculated from case-control data.

● However, for most case-control studies, we can calculate the AR% and PAR%.


AR & AR% in Case-Control Studies

• No direct risk estimates in case-control study- No calculation of AR (risk difference) and AR% possible

• If odds ratio approximates relative risk, then

100 x OR

1 -OR AR% =

AR% (Case-Control Studies)AR% (Case-Control Studies)

(OR – 1)

AR% = ----------- x 100

OR

Example: AR% (Case-Control Studies)Example: AR% (Case-Control Studies)

Smoke Yes No

Yes 160 120

No 90 200

Case-control study to evaluate the impact of smoking as related to bladder cancer.

Bladder Cancer(160 / 90)

OR = ------------

(120 / 200)

= 2.96


Question: Among smokers, what proportion (percent) of bladder cancer cases can be attributed to their smoking habit?

(OR – 1)AR% = ----------- x 100

OR

AR% = ((2.96 – 1) / 2.96) x 100 = 66.2%


● 66% of bladder cancer cases among smokers can be attributed to their smoking.

● 66% of bladder cancer cases among smokers could be prevented if they had never taken up smoking.

(Assuming there is a causal association between smoking and the development of bladder cancer).

PAR% (Case-Control Studies)PAR% (Case-Control Studies)

(PE) (OR – 1)

PAR% = -------------------- x 100

[(PE) (OR-1)] + 1

where PE = proportion of exposed controls

(assuming that the proportion of exposed controls is representative of the proportion exposed in the source population)

Example: PAR% (Case-Control Studies)Example: PAR% (Case-Control Studies)

Smoke Yes No

Yes 160 120

No 90 200

Case-control study to evaluate the impact of smoking as related to bladder cancer.

Bladder Cancer (160 / 90)

OR = ------------

(120 / 200)

= 2.96

PE = 120 / 320 = 0.375


Question: In this study population, what proportion (percent) of bladder cancer cases can be attributed to smoking?

(PE) (OR – 1)

PAR% = ---------------------- x 100[(PE) (OR-1)] + 1

PAR% = (0.375) (2.96-1) [(0.375) (2.96-1)] + 1

x 100 = 42.4%


● In this study population, 42% of bladder cancer cases can be attributed to smoking.

● In this study population, 42% of bladder cancer cases could be prevented if people would not take up smoking.

(Assuming there is a causal association between smoking and the development of bladder cancer).

PAR% in Cohort & Case-Control Studies

• Cohort study

• Case-control studyIf % controls exposed ≈ % population exposed:

where P = % population exposed

where Pcon = % controls exposed

100 x 1 1)-(RR P

1) -(RR P PAR%

+=

100 x 1 1)-(OR P

1) -(OR P PAR%

con

con

+=

Prevented Fraction (PF)

• If relative risk <1- Proportion of potential new cases which would have

occurred if the exposure had been absent- Proportion of potential cases prevented by the exposure

RR -1

I

I -I PF

unexposed

exposed unexposed

=

=

PF: Vaccine efficacy

Pop. Cases Cases/1000 RR

Vaccinated 301,545 150 0.49 0.28

Unvaccinated 298,655 515 1.72 Ref.

Total 600,200 665 1.11

0.72 0.28 - 1

0.72 1.72

0.49 - 1.72 PF

==

==

Annual Death Rates for Lung Cancer and Coronary Heart Disease

by Smoking Status, Males

1000 – 500 = 500 per 100,000

127.2 – 12.8 = 114.4 per 100,000

AR

1000 / 500 = 2127.2 / 12.8 = 9.9RR

50012.8Non-smoker

1,000127.2Smoker

Coronary Heart DiseaseLung CancerExposure

Annual Death Rate / 100,000

Summary

The risk associated with smoking is lower for CHD (RR=2) than for lung cancer (RR=9.9)

Attributable risk for CHD (AR=500) is much higher than for lung cancer (AR=114.4)

In conclusion: CHD is much more common (higher incidence) in the population, thus the actual number of lives saved (or death averted) would be greater for CHD than for lung cancer

Gerstman Chapter 8 (partial) 57

Comparison of RR and RD

Lung Cancer and CHD mortality in smokers and non-smokers (per 100,000 person-years)

Smokers

Non

smokers RR RD

LungCA

104 10 10.40 94

CHD 565 413 1.37 152

Smoking causes more heart disease

Smoking has a stronger association with lung cancer

An exposure can have a strong relative effect (RR) An exposure can have a strong relative effect (RR) but make a small difference in absolute terms (RD)but make a small difference in absolute terms (RD)


Relative Risk: Measure of the strength of association, and indicator used to assess the possibility of a causal relationship.

Attributable Risk: Measure of the potential for prevention of disease if the exposure could be eliminated (assuming a causal relationship).


Relative Risk:

• Etiology

Attributable Risk:

• Policy decisions

• Funding decisions (e.g. prevention programs)

Summary – Measures of PublicSummary – Measures of PublicHealth ImpactHealth Impact

Measure

Cohort

study

Population-based case-

control study

Other type of case-control

study

AR Yes Yes No

AR% Yes Yes Yes

PAR Yes Yes No

PAR% Yes Yes Yes

Ringkasan ukuranTipe

Kuantitas Matematis

Tanpadenominator

Dengan denominator

EnumerasiHitung,

angka mutlakRasio Proporsi Rate

Ringkasan ukuranTipe

Kuantitas Matematis

Enumerasi Rasio Proporsi Rate

•RR•OR•IDR

•%•AR%•PAR%

•Crude•Spesific•Adjusted

Ringkasan ukuran

Ukurandalam

epidemiologi

UkuranFrekuensiPenyakit

Ukuran asosiasi

Ukuran efek/dampak

Ukuran frekuensi penyakit

Ukuran frekuensiPenyakit

Insidens Prevalens

Insidens Kumulatif

Incidence Density

Prevalens titik

Prevalens periode

Mortalitas


UkuranRasio

Risk Ratio

Odds Rasio

Insidence DensityRatio

Prevalence Ratio


UkuranEfek

/dampak

Perbedaan efek

FraksiEfek

RDARERPAR

AR% PAR% PF

RD = Risk Difference

AR = Attributable Risk

ER = Excess Risk

PAR = Population Attributable Risk

PF = Prevented Fraction

AR=Attributable Risk

• Utk menentukan proporsi dari outcome (penyakit) pada grup exposed yg memang betul-betul disebabkan oleh E

• AR individu = RR - 1/RR• PAR (Population AR)

= Pe (RR-1)

1 + Pe (RR-1)

Pe = proporsi populasi yang terexpose

Gerstman Chapter 8 (partial) 68

Epidemiology Kept Simple

Chapter 8 Measures of Association

If it’s not clear…

• Gordis Leon, M.D., M.P.H., Dr.P.H. 2009. Epidemiolgy. W.B. Saunders Company. Philadelphia ,Chapter 12

• Epidemiology in Medicine. Henneckens CH, Buring JE. Edited by Mayrent SL, Chapter 4

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Sesi 5 b ukuran dampak.2009l