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UKURAN ASOSIASI DALAM EPIDEMIOLOGI Nurul Wandasari Singgih Prodi Kesehatan Masyarakat Univ Esa Unggul 2012/2013.

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Presentasi berjudul: "UKURAN ASOSIASI DALAM EPIDEMIOLOGI Nurul Wandasari Singgih Prodi Kesehatan Masyarakat Univ Esa Unggul 2012/2013."— Transcript presentasi:

1 UKURAN ASOSIASI DALAM EPIDEMIOLOGI Nurul Wandasari Singgih Prodi Kesehatan Masyarakat Univ Esa Unggul 2012/2013

2 Tipe ukuran yang digunakan dalam epidemiologi Ukuran asosiasi – Merefleksikan kekuatan atau besar asosiasi antara suatu eksposur/faktor risiko dan kejadian suatu penyakit – Memasukkan suatu perbandingan frekuensi penyakit antara dua atau lebih kelompok dengan berbagai derajat eksposur – Beberapa ukuran assosiasi digunakan untuk mengestimasi efek

3 Basic Question in Analytic Epidemiology Are exposure and disease linked? ExposureDisease

4 Ukuran-ukuran asosiasi Ukuran rasio (perbandingan relatif) – rasio dua frekuensi penyakit membandingkan kelompok terpajan dengan kelompok tidak terpajan Ukuran perbedaan efek (perbandingan absolut) – perbedaan antara ukuran frekuensi penyakit suatu kelompok terpajan dan kelompok yang tidak terpajan

5 Two-By-Two Table ab cd Disease Yes No Yes Exposure No Total a+c b+d Total a+b c+d a+b+c+d

6 Hypothetical Two-By-Two Table Lung cancer Yes No Yes Smoking No Total 85 1,000 Total ,085

7 Relative Risk (RR) Measures how likely the exposed group will develop a disease compared to the unexposed group. RR = incidence in the exposed = a/(a+b) incidence in the unexposed c/(c+d)

8 Example: Hypothetical Study Lung cancer YesNoTotal Yes SmokingNo Total851,0001,085

9 Relative Risk = 70/(70+300) = /(15+700) Which means… participants who smoked were 9 times more likely to develop lung cancer than those who did not smoke.

10 Interpreting Measures of Association RR of 1.0 indicates that the occurrence of disease in the exposed an unexposed groups are identical: – No association observed between exposed and unexposed groups.

11 Interpreting Measures of Association (Continued) RR greater than 1.0 indicates a positive association, or an increased risk among the exposed. RR less than 1.0 means that there is a decreased risk among the exposed group.

12 Ukuran-ukuran asosiasi Ukuran rasio – Rasio risiko atau risiko relatif (RR) –Rasio Insidens Kumulatif (RIK)

13 Perhitungan RR untuk CI Outcome (+)Outcome (-)Total E (exposed)aba + b NE (unexposed)cdc + d Totala + cb + dN (a + b + c + d) CI pada populasi exposed (E) --- a/(a + b) RR= CI pada populasi unexposed (NE) --- c/(c + d)

14 THEN,FOLLOW TO SEE WHETHER Totals Incidence rates of Disease Disease Develops Disease Does Not Develop Exposedaba + b Not Exposed cdc + d FIRST, SELECT a a+b c c+d Incidence in exposed Incidence in non-exposed = = a a+b c c+d Relative Risk ( RR ) = incidence in exposed incidence in non-exposed =

15 A Prospective Study of 3,000 Smokers and 5,000 Non- smokers to Investigate Smoking and Coronary Heart Disease (CHD) Example : Develop CHD Do Not Develop CHD Total Incidence per 1,000 per year Healthy Smokers842,9163, Healthy Non-Smokers874,9135, THEN FOLLOW UP TO SEE HOW MANY FIRST, SELECT

16 Contoh 5. Tabel 1. Kaitan antara merokok dan angka insidens stroke dalam suatu kohort. Kategori merokok Jumlah kasus stroke Orang-tahun observasi (lebih dari 8 tahun) Tingkat insidens stroke (per orang tahun) Tidak pernah merokok ,7 Mantan perokok ,9 Perokok ,6 Total ,2 Sumber: diterjemahkan dari:Beaglehole et al. Basic Epidemiology. WHO

17 Postmenopausal Hormone Supplement and CHD CHDPerson-years Ever use3054,308.7 Past use1924,386.7 Current1129,922.0 Never use6051,477.5 RR ever use vs never use = (30/54,308.7) / ( 60/ ) = 0.5 RR past use vs never use = (19/ ) / (60/ ) = 0.7 RR current use vs never use = (11/ ) / (60/ ) = 0.3

18 Ukuran-ukuran asosiasi Ukuran rasio – Rasio odds (Odds ratio = OR) Nama lain: Odds relative; rasio kros-produk rasio dua odds yang digunakan dalam studi kasus- kontrol untuk mengestimasi rasio rate atau rasio risiko

19 Ukuran-ukuran asosiasi Ukuran rasio – Rasio odds (Odds ratio = OR) odds untuk satu kelompok dibagi dengan odds untuk kelompok yang lain Mempunyai interpretasi yang sama seperti risiko relatif

20 Ukuran-ukuran asosiasi Odds suatu kejadian – rasio probabilitas bahwa kejadian terjadi terhadap probabilitas kejadian tidak terjadi P = Probabilitas suatu kejadian terjadi 1 – P= Probabilitas suatu kejadian tidak terjadi

21 Figure 11-5 A, Odds ratio (OR) in a cohort study. B, Odds ratio (OR) in a case-control study. Downloaded from: StudentConsult (on 8 October :44 AM) © 2005 Elsevier

22 Prevalence Odds Ratio (POR) = Cross Product Ratio  bila data didasarkan pada kasus-kasus prevalens FaktorKasusKontrolTotal Perokok650 (a) 950 (b)1600 Bukan perokok 50 (c) 350 (d) 400 Total

23 Odds Ratio & Risk Ratio The odds ratio will provide a good estimate of the risk ratio when: 1.The outcome (disease) is rare D+D+ D-D- E+E+ ab E-E- cd OR = (a / c) / (b / d) OR = (ad) / (bc) a / (a +b ) RR = c / (c +d) If the disease is rare, then cells (a) and (c) will be small a / (a +b )a / b ad RR = = =-- = OR c / (c +d)c / d bc

24 Figure 11-6 Example: The odds ratio is a good estimate of the relative risk when a disease is infrequent. Downloaded from: StudentConsult (on 8 October :44 AM) © 2005 Elsevier

25 Figure 11-7 Example: The odds ratio is not a good estimate of the relative risk when a disease is not infrequent. Downloaded from: StudentConsult (on 8 October :44 AM) © 2005 Elsevier

26 In a prospective study/cohort study, the Relative Risk can be calculated directly In a retrospective study /case control study, the RR cannot be calculated directly, so that the Relative Odds or ODDS RATIO ( Cross Products Ratio ) is used as an estimate of the RR, when the risk of the disease is low

27 OR & RR Pada penyakit yang jarang terjadi,nilai Odds Ratio hampir sama dengan nilai Relative Risk (Risk Ratio). Nilai Prevalence Odds Ratio hampir sama dengan nilai Prevalence Proportion Ratio. Pada penyakit yang umum terjadi, nilai Odds Ratio lebih ekstrim dari pada Risk Ratio.

28 GerstmanChapter 8 (partial)28 Interpretation of Odds Ratio Relative odds associated with exposure OR = 1  no association OR > 1  positive association OR < 1  negative association Size of OR indicates strength of association OR ≈ RR when disease rare (i.e., risk < 5%); when disease not rare, OR still a valid measure of association


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