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DESAIN STUDI EPIDEMIOLOGI ANALITIK

DESAIN STUDI EPIDEMIOLOGI ANALITIK. APRININGSIH, SKM, MKM. Types of epidemiological study. Discriptive : * Case report * Case series * Cross-sectional * Ecological Analytic: * Observational: - Case-control - Cohort * Experimental: intervention.

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DESAIN STUDI EPIDEMIOLOGI ANALITIK

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  1. DESAIN STUDI EPIDEMIOLOGI ANALITIK APRININGSIH, SKM, MKM

  2. Types of epidemiological study • Discriptive : * Case report * Case series * Cross-sectional * Ecological • Analytic: * Observational: - Case-control - Cohort * Experimental: intervention

  3. CASE CONTROL STUDIESSOME KEY POINTS CASE CONTROL STUDIESSOME KEY POINTS • Most frequently used study design • Participants selected on the basis on whether or not they are DISEASED (remember in a cohort study participants are selected based on exposure status) • Those who are diseased are called CASES • Those who are not diseased are called CONTROLS

  4. Study Population DISEASED non-DISEASED (Cases) (Controls)

  5. Source population Exposed Unexposed

  6. Source population Exposed Cases Unexposed

  7. Source population Exposed Sample Cases Unexposed Controls

  8. Source population Cases Exposed Sample Unexposed Controls = Sample of the denominator Representative with regard to exposure Controls

  9. Case control study Exposure ? ? Disease Controls Retrospective nature

  10. SELECTION OF CASES • FIRST decide on a specific case definition based on a medically diagnosed condition • Must consider what criteria will confirm the case definition • lung cancer confirmed by biopsy • osteoporosis confirmed by bone density measurements • atherosclerosis confirmed by ultrasound of carotid arteries

  11. SELECTION OF CASES • SECOND will you use INCIDENT or PREVALENT cases? • Incident… • must wait for new cases to occur • study can specifically measure exposure relating to development of disease • Prevalent... • don’t have to wait while cases occur with time - more practical! • study will specifically measure exposure relating to survival with disease

  12. SELECTION OF CASES • THIRD be aware of the unique qualities of certain groups • hospital admissions • nursing homes • screening participants • day care facilities • some groups may have better supporting medical records • some groups may be more homogenous and present less confounding variables

  13. SELECTION OF CONTROLS • THE BIG PICTURE… • Controls should be representative of the referent population from which cases are selected (I.e. comparable) • They don’t have to be representative of the source (I.e. total) population • Controls should have the potential to become cases (they have to be susceptible for the disease of interest)

  14. TotalPopulation Reference Population Cases Controls Controls should be comparable to cases

  15. SELECTION OF CONTROLS • Different Types of Controls… • randomly selected individuals from the population like RDD (random digit dialing) • individuals that live in the same neighborhoods as cases

  16. SELECTION OF CONTROLS • Different Types of Controls( con’t)… • best friends of cases • spouses or siblings of cases • individuals at the same hospital with cases

  17. What would be a good sources of controls for …? • Investigating whether risk of cancer was associated with a local chemical manufacturing company . . . • Investigating whether heart disease was associated with cultural or family dietary patterns . . .

  18. MEASURING ASSOCIATION • because study participants in Case Control studies are selected based on disease status... • case control studies are ideal for the study of rare diseases • incidence can’t be calculated

  19. MEASURING ASSOCIATION • Because incidence can’t be calculated, a relative risk can’t be calculated (RR is a ratio of INCIDENCE in exposed and non-exposed) • Instead of the RR, an ODDS RATIO is calculated in case control studies 19

  20. MEASURING ASSOCIATION • Odds: NOT a proportion, but the ratio of the # ways an event CAN occur relative to the # of ways an event CAN NOT occur Odds = P(event occurs) = p / ( 1 - p) 1 - P(event occurs) • Odds Ratio: Odds of case being exposed Odds of control being exposed 20

  21. Classic 2 x 2 Table Disease No Disease Exposure a b No Exposure c d Odds Ratio = a/c = a d b/d b c 21

  22. Is Use of Artificial Sweeteners associated with Bladder Cancer? Cases Controls Ever Used 1,293 2,455 Never Used 1,707 3,321 Total 3,000 5,776 ODDS RATIO = 1,293 * 3,321 = 1.026 2,455 * 1,707 Hoover and Strasser (1980) Lancet 1: 837-840

  23. Interpretation of the Odds Ratio… If O.R. = 1 then exposure NOT related to disease OR >1 then exposure POSITIVELY related to disease OR <1 then exposure NEGATIVELY related to disease Hoover and Strasser concluded what from their study?

  24. A Special Case... When the disease is RARE and the duration of the given disease SHORT…. O.R.  R.R.

  25. CASE CONTROL STUDY SUMMARY • cases and controls are • representative of a referent • population • controls have the potential • to become cases • selection based on disease • and exposure assessed • retrospectively cases Referent pop’n Total population

  26. SELECTION OF CONTROLS • to avoid potential problems of confounding some studies use MATCHING • MATCHING: the process of selecting controls so that they are similar to cases on certain specific characteristics

  27. SELECTION OF CONTROLS • CHARACTERISTICS THAT ARE OFTEN USED FOR MATCHING… • age • gender • body mass index (weight / height2) • smoking status • marital status

  28. SELECTION OF CONTROLS • There are two types of matching… • GROUP MATCHING (frequency matching) • based on proportions • Idea is to select a control group with a certain characteristic identical to cases in the same proportion as it appeared in cases Example: if 25% of cases in your study smoke you would select a control population that included 25% smokers

  29. SELECTION OF CONTROLS • There are two types of matching… • INDIVIDUAL MATCHING (matched pairs) • for every individual case a control is selected who is identical to the case on certain characteristics Example: If your first case is a 25 year-old woman who smokes then you would find a control who is 25, female and a smoker

  30. MATCHED PAIRS EXAMPLE control case case control

  31. Cohort study is the gold standard of analytical epidemiology Alain Moren Case-control studies have their place in epidemiology, but if cohort study is possible do not settle for second best

  32. krisbantas/studi kohort/S2

  33. Studi Kohort Prospektif • Prospective cohort study : • nama lain : • concurrent cohort study • longitudinal study • Struktur : • peneliti memilih sampel (kelompok kohort) • yang akan diteliti dari populasi • ukur status “exposure” pada anggota sampel • sehingga menjadi sampel menjadi 2 kelompok • kelompok dengan “E” + • kelompok dengan “E” - • follow-up kedua kelompok selama periode waktu • tertentu • ukur status “disease” pada anggota sampel dari • kedua kelompok kohort • bandingkan

  34. dari pengamatan yang dilakukan , diperoleh informasi : • insiden dari “outcome” (sakit, meninggal dll) • riwayat alamiah penyakit • analisa hubungan antara • “predictor variable” dan “outcome variable” • “exposure” “disease” • disain : • The Present The Future Disease + Disease - Disease + Disease - Risk factor “E” + Risk factor “E” - populasi o Follow -up sampel

  35. contoh : • suatu studi ingin menentukan apakah olah raga • dapat mencegah penyakit jantung koroner (PJK) • kelompok kohort yang diteliti terdiri dari 16.936 • (dokter) • variabel “exposure”: olah raga • olah raga teratur ( E+) • tidak olah raga ( E -) • Follow-up cohort 10 tahun • variabel “outcome” meninggal karena PJK • hasil : • Insiden pada kelompok E + = 24/10.000 person-year • insiden pada kelompok E - = 16/10.000 person-year • 24/10.000 • RR = -------------------- = 1.5 • 16/10.000

  36. Kelebihan dan Kelemahan Studi Kohort prospektif • Kelebihan : • sangat cocok untuk studi yang ingin melihat : • gambaran insiden penyakit • kausa atau faktor risiko • (studi dimulai dari pengukuran faktor • risiko sebelum “outcome” muncul) • memberi kesempatan pada peneliti mengukur • variabel yang diteliti, lebih akurat dan komplit • no recall bias • Kelemahan : • mahal • tidak efisien • ada efek dari konfounder

  37. Studi Kohort Retrospektif • Nama lain : • retrospective cohort study • non concurrent cohort study • hystorical cohort study • Stuktur : • strukturnya sama dengan studi kohort prospektif • bedanya, pada studi kohort retrospektif : • pengukuran variabel prediktor, data dasar • follow-up dilakukan pada masa lalu • pengukuran terhadap variabel “outcome” • dapat dilakukan : • saat studi dimulai • dari data masa lampau • pada prinsipnya pengukuran variabel “outcome” • dilakukan setelah pengukuran variabel “predictor”

  38. disain : • The Past The Present Disease + Disease - Disease + Disease - Risk factor “E” + Risk factor “E” - sampel populasi

  39. Langkah-langkah studi : • tentukan kelompok kohort yang akan diteliti • (data dari masa lampau) • kumpulkan data mengenai variabel “predictor” • atau “exposure” (data dari masa lampau) • follow-up kelompok kohort • kumpulkan data variabel “outcome” (data dapat • diperoleh : • dari masa lampau • pada saat penelitian • Kalkulasi : • Insiden “D” pada kelompok “E”+ • RR= ---------------------------------------------------- • Insiden “D” pada kelompok “E” -

  40. Contoh : • suatu studi ingin melihat prognosa dari prolaps katup • mitral dengan kelainan tambahan • ditentukan kelompok kohort yang akan diteliti • 343 pasien dengan kelainan prolaps katup mitral • ( data dari pemeriksaan EKG tahun 1975 dan 1979) • dikumpulkan data menegenai variabel “predictor”” • data dari medical record • variabel “predictor” berupa kelainan tambahan • pada prolapsus katup mitral (data EKG) • dikumpulkan data mengenai variabel “outcome” • variabel “outcome” yang diukur berupa : • mati tiba-tiba • emboli • endokarditis

  41. hasil : 10% dari pasien -pasien prolaps mitral dengan kelainan tambahan pada katup mitral meninggal tiba-tiba0.7 % dari pasien tanpa kelainan tambahan Padakatup mitral meninggal tiba-tiba Insiden E+ 10 RR = -------------------- = ---------- = 14 Insiden E - 0.7

  42. Kelebihan dan kelemahan studi kohort retrospektif • Kelebihan : • seperti studi kohort prospektif • variabel “predictor” diukur sebelum variabel • “outcome” • pengukuran variabel “predictor” tidak bias karena • diukur sebelum variabel “outcome” diukur • tidak ada pengaruh yang disebabkan telah • diketahuinya “outcome” (spt pada studi kasus- • kontrol) • lebih hemat waktu, dana • Kelemahan : • peneliti tidak dapat mengontrol kualitas data yang • dipakai

  43. Nested Case-Control • Merupakan studi kasus kontrol di dalam studi kohort • Studi kasus kontrol yang disarangkan pada studi kohort • Stuktur : • pengukuran variabel “predictor”pada partisipan • telah dikumpulkan dimasa lampau (kemudian disimpan) • semua partisipan di follow-up • pada akhir penelitian, diukur variabel “outcome” • kelompok dengan “outcome” / disease + • kelompok dengan “outcome” / disease - • kemudian pada kelompok “disease +” (case) dan • “disease -”(control) masing-masing dilihat kembali • nilai dari pengukuran variabel “predictor” pada masa • lalu • bandingkan “exposure” pada kedua kelompok kasus • dan kontrol

  44. Contoh : • Suatu studi ingin melihat apakah kadar mikronutrien • X dalam darah ada hubungannya dengan kejadian • penyakit kanker • pengambilan sampel darah telah dilakukan 10 tahun • yang lalu pada 1000 orang • pada saat penelitian terdapat 50 penderita kanker, 950 • tetap sehat • kemudian dilakukan pemeriksaan terhadap sampel • darah yang telah diambil • dari 50 penderita kanker 25 diantaranya mempunyai • kadar mikronutrien X yang rendah • dari 950 yang sehat, 300 diantaranya mempunyai • kadar mikronutrien X yang rendah

  45. Kasus 100 40 (Kadar mikronutrien X rendah) 60 Kadar mikronutrien X normal) Kontrol 300 (Kadar mikronutrien X rendah) 900 600 (Kadar mikronutrien X normal) 40/60 OR = --------------- = 1.3 interpretasi Kadar mikronutrien X yang rendah dalam darah berisiko 1.3 x menimbulkan kanker dari pada bila kadarnya normal 300/600

  46. Studi Kohort Tunggal / Single-cohort study • Struktur : • kelompok kohort terdiri dari 2 sampel kelompok • kohort atau lebih dengan status keterpaparan • dengan “exposure” yang berbeda-beda • sampel kohort berasal dari 1 populasi yang sama • variabel “predictor” diukur sebelum variabel “outcome” • diukur • dapat bersifat kohort retrospektif atau prospektif

  47. Disain : The Present The Future Disease + Disease - Sample Sampel Risk factor “E” + Disease + Disease - Risk factor “E” - population

  48. Studi Kohort Ganda / Double-cohort study • Struktur : • kelompok kohort terdiri dari 2 kelompok atau lebih • sampel kohort berasal dari 2 populasi atau lebih • yang berbeda-beda level keterpaparannya dengan • faktor risiko • variabel “predictor” diukur sebelum variabel “outcome” • diukur • dapat bersifat kohort retrospektif atau prospektif

  49. Disain : The Present The Future Disease + Population ( risk factor +) Risk factor “E” + sample sample Disease - Follow-up Disease + Population ( risk factor -) Risk factor “E” - Disease -

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