Measures of Association

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1 Measures of Association
Max Sanam FKH Undana

2 Risiko Risiko adalah probabilitas terjadinya suatu peristiwa
Suatu keadaan atau faktor yang menentukan terjadi atau tidak terjadinya suatu hal dinamakan faktor risiko Pecah ban merupakan faktor risiko bagi kejadian kecelakaan kendaraan bermotor Hipertensi adalah faktor risiko bagi penyakit jantung koroner. Vaksinasi adalah suatu faktor risiko protektif yang biasanya menurunkan risiko penyakit

3 Jika kita mengidentifikasi berbagai faktor risiko yang memiliki hubungan kausatif dengan kemungkinan meningkat atau menurunnya suatu penyakit Hasilkan rekomendasi bagi pengelolaan kesehatan. Riset epidemiologis estimasi dan kuantifikasi faktor-faktor risiko dari penyakit.

4 Asoasiasi antara faktor risiko (paparan) dan outcome (biasanya penyakit) dapat diselidiki menggunakan studi-studi observasional Bayangkan suatu studi dimana pada awalnya subjek bebas penyakit dan kemudian dimonitor selama periode waktu tertentu untuk melihat kejadian penyakit

5 Jika kedua variabel paparan (exposure) dan outcome bersifat biner (ya atau tidak), hasilnya dapat disajikan dalam suatu tabel 2 × 2. Berbagai ukuran asosiasi dapat dikalkulasi: (1) measures of strength, (2) measures of effect, and (3) measures of total effect. Diseased Non-diseased Total Exposed a b a+ b Non-exposed c d c+ d a + c b+ d a+b+c+d = n

6 Incidence risk in the exposed population: RE = a/(a + b)
Diseased Non-diseased Total Exposed a b a+ b Non-exposed c d c+ d a + c b+ d a+b+c+d = n Incidence risk in the exposed population: RE = a/(a + b) Incidence risk in the non-exposed population: RO = c/(c + d) Incidence risk in the total population: RTotal = (a + c)/(a + b + c + d) Odds of disease in the exposed population: OE = a/b Odds of disease in the non-exposed population: OO = c/d

7 Ukuran-Ukuran Kekuatan
Risk ratio (RR) RR didefinisikan sebagai rasio risiko penyakit (i.e. the incidence risk) di dalam kelompok terpapar terhadap risiko penyakit di dalam kelompok tidak terpapar RR = RE / RO RR memberikan estimasi berapa banyak kali kemungkinan bagi individu yang terpapar untuk mengalami penyakit dibandingkan individu yang tidak terpapar faktor risiko Jika risk ratio = 1, maka risiko sakit di dalam kelompok terpapar dan tidak terpapar adalah sama

8 Risk Ratio ... Jika RR > 1, maka exposure meningkatkan ririko kejadian penyakit Jika RR < 1, exposure menurunkan risiko kejadian penyakit dan disimpulkan sebagai protektif. Risk ratio cannot be estimated in case-control studies, as these studies do not allow calculation of risks. Pada CC study, Odds ratios (OR) yang digunakan dan bukan RR Nilai RR berkisar antara 0 dan tak terhingga.

9 Odds ratio The odds ratio is the odds of disease, given exposure.
The odds ratio (OR) is an estimate of risk ratio and is interpreted in the same way. OR is calculated as: OR = OE / OO = ad / bc When the number of cases of disease is low relative to the number of non-cases (i.e. The disease is rare), then the odds ratio approximates risk ratio.

10 Ukuran-ukuran Dampak di dalam Populasi terpapar
Attributable risk (rate) Attributable risk (or rate) is defined as the increase or decrease in the risk (or rate) of disease in the exposed group that is attributable to exposure. AR (unlike RR) describes the absolute quantity of the outcome measure that is associated with the exposure AR is calculated as: AR = RE − RO

11 Attributable fraction (AF)
AF (attributable proportion in exposed subjects) is the proportion of disease in the exposed group that is due to exposure. AF is calculated as: AF = (RE − RO) / RE = (RR − 1) / RR For case-control studies, AF can be approximated: AFest = (OE − OO) / OE = (OR − 1) / OR

12 Suatu studi Kasus-Kontrol : efek vaksinasi oral terhdap ada atau tidaknya rabies pada srigala.
odds rabies kelompok tidak divaksinasi adalah 2.3 odds rabies kelompok vaksinasi (OR = 2.30). Lima puluh enam % kasus rabies pada srigala yang tidak divaksinasi adalah karena tidak divaksinasi (AF est = 0.56). Rabies + Rabies - Total Vaccination - 18 30 48 Vaccination + 12 46 58 76 106

13 Ukuran-Ukuran Efek pada Populasi
Population attributable risk (rate) PAR is the increase or decrease in risk (or rate) of disease in the population that is attributable to exposure. PAR is calculated as: PAR = RTotal − RO

14 Population attributable fraction (also known as the aetiologic fraction) is the proportion of disease in the population that is due to the exposure. PAF = (R Total − RO) / R Total

15 FUS + FUS - Total DCF + 13 2163 2176 DCF - 5 3349 3354 30 5512 5530
Suatu studi Potong-Lintang diterapkan menyelidiki hubungan antara dry cat food (DCF) and feline urologic syndrome (FUS) Hasil penelitian sbb: FUS + FUS - Total DCF + 13 2163 2176 DCF - 5 3349 3354 30 5512 5530

16 The incidence risk of FUS in the DCF+ group was 5.97 cases per 1000.
Total DCF + 13 2163 2176 DCF - 5 3349 3354 30 5512 5530 The incidence risk of FUS in the DCF+ group was 5.97 cases per The incidence risk of FUS in the DCF- group was 1.49 cases per 1000. The incidence risk of FUS in DCF exposed cats was 4.01 times greater than the incidence risk of FUS in DCF- cats (RR = 4.0). The incidence risk of FUS in DCF+ cats that may be attributed to DCF is 4.5 per 1000 (AR = ). In DCF+ cats 75% of FUS is attributable to DCF (AF = 0.75).

17 FUS + FUS - Total DCF + 13 2163 2176 DCF - 5 3349 3354 30 5512 5530 The incidence risk of FUS in the cat population that may be attributed to DCF is 1.8 per 1000. That is, we would expect the risk of FUS to decrease by 1.8 cases per if DCF were not fed (PAR = ). Fifty-four percent of FUS cases in the cat population are attributable to DCF (PAF = 0.54).

18 Penggunaan ukuran-ukuran dampak secara tepat
Parameter Case-Control Cohort Cross-sectional Measures of strength: RR No Yes Yes (Prevalence RR) OR Yes (Prevalence OR) Measures of effect: AR AF AFest Measures of effect in population (total effect): PAR PAF PAFest