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Frequency and Measures of Association

Frequency and Measures of Association. DESCRIPTIVE EPIDEMIOLOGY. ANALYTIC EPIDEMIOLOGY. Incidence Prevalence. Risk Factors. Triad Epidemiology Host – Agent - Environment. Diagnostic Tools. Holistic Diagnosis (BIOPSYCHOSOSIAL). CLINICAL EPIDEMIOLOGY

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Frequency and Measures of Association

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  1. Frequency and Measures of Association

  2. DESCRIPTIVE EPIDEMIOLOGY ANALYTIC EPIDEMIOLOGY Incidence Prevalence Risk Factors Triad Epidemiology Host – Agent - Environment Diagnostic Tools Holistic Diagnosis (BIOPSYCHOSOSIAL) CLINICAL EPIDEMIOLOGY (Prognostic Study, Clinical Trial, Meta Analysis) Therapy, Prognosis

  3. Lecture Contents • Association • - Relative risk • - Rate ratio • - Risk ratio • - Odds ratio • - Risk difference • Frequency • Prevalence • Incidence • Cumulative • Density • Precision • P value • Confidence level

  4. Frequency Measures • Two types: • Someone has the disease already: PREVALENCE • Someone gets the disease in the future: INCIDENCE

  5. Study Design Direction of inquiry Survey / Cross Sectional TODAY Cohort Case-control Historical cohort

  6. Prospective Cohort Exposure Outcome Start here + ** Free of outcome - * + - to t1

  7. Historical Cohort Exposure Outcome Start here + ** Free of outcome - * + - to t1

  8. Case ControlStart here Exposure Outcome + Case - Population + Control -

  9. RASIO DAN PROPORSI RASIO • PERBANDINGAN SECARA UMUM • TAK ADA KAITAN PEMBILANG DAN PENYEBUT PROPORSI • PEMBILANG MERUPAKAN BAGIAN DARI PENYEBUT A/B A/(A+B)

  10. Frequency measures: diagnostic research • Suppose: you see a patient with symptoms that possibly point at arthritis • Research question ?

  11. Frequency measures: diagnostic research • Suppose: you see a patient with symptoms that possibly point at venous thrombosis • Research question: What is the probability of arthritis given the physical exam / tests?

  12. Frequency measures: prevalence • Cross-sectional studies • Determinant and disease measured at the same time • Prevalence • Number of persons with the disease at a certain moment

  13. Frequency measures: prevalence • Prevalence (%) = Number of persons with the disease Total population Numerator is part of denominator

  14. ANGKA POINT PREVALENSI S KASUS (BARU+LAMA) SATU SAAT SSELURUH POPULASI SAAT ITU MERUPAKAN NILAI PROPORSI PADA SATU SAAT TERTENTU GUNA EVALUASI PENGOBATAN

  15. POINT PREVALENCE • Tujuan : mengetahui prevalensi artritis di suatu komunitas di suatu hari tertentu • Hari itu kita lakukan kunjungan dari rumah ke rumah untuk melakukan anamnesis dan pemeriksaan fisik untuk menentukan berapa orang yang mengalami artritis pada hari itu Prevalensi (point) = Jumlah orang yang mengalami artritis hari itu Jumlah penduduk di komunitas hari itu

  16. PERIOD PREVALENCE SBARU+LAMA SUATU PERIODE SSELURUH POPULASI PERIODE TERSEBUT

  17. Frequency measures: prevalence • Examples • 50% of the persons with a suspicion of lung cancer had a lesion on the thorax X-ray • In a general practice population of 2500 persons, 50 had asthma • 30% of the Dutch people smoke

  18. Frequency measures: prognostic research • Suppose: You see a patient diagnosed as MCI post CABG who asks for her prognosis • Research question?

  19. Frequency measures: prognostic research • Suppose: You see a patient diagnosed as MCI post CABG who asks for her prognosis • Research question: What is the probability that I die within 5 years / get a relapse?

  20. ANGKA INSIDENSI SKASUS BARU DLM SUATU PERIODE SPOPULASI RENTAN DLM PERIODE TERSEBUT POPULASI RENTAN = BEBAS KASUS MENURUT PERIODE WAKTU PENYEBUT = POPULASI RENTAN (memiliki kemungkinan untuk menjadi kasus) EVALUASI PENCEGAHAN

  21. Incidence per 1000 = • Incidence per 10.000 = SKASUS BARU DLM SUATU PERIODEX 1000 S POPULASI RENTAN DLM PERIODE TERSEBUT SKASUS BARU DLM SUATU PERIODEX 10000 S POPULASI RENTAN DLM PERIODE TERSEBUT

  22. Frequency measures: Incidence • Incidence • Number of new cases • In the population at risk • Two types of incidence • Cumulative Incidence Risk (CIR) • Incidence Density Rate (IDR)

  23. Cumulative Incidence Risk (CIR) calculation a /(a +b) = CIR outcome in expose c /(c +d) = CIR outcome in non expose

  24. Calculate : • CIR death post CABG MCI anterior/inferior ? • CIR death pada post CABG non MCI ant./inf ?

  25. CIR death post CABG MCI anterior/inferior ? • 8/29 = 0.2759 = 27.59% • CIR death pada post CABG non MCI ant./inf ? • 12/109 = 0.1101 = 11.01%

  26. Frequency measures: Incidence • Cumulative incidence • new cases in a certain time period in the population at risk (free of the disease/outcome at the start) • proportion / probability • varies between 0 and 1 • within certain time period

  27. Frequency measures: Incidence • Cumulative incidence: examples • 5-year risk of a second MI • 10-year survival for women with breast cancer • 1-year risk of a fracture for osteoporotic women

  28. Frequency measuresIncidence • Incidence Density = number new patients person-years of the population at risk • 10 per 1000 person-years (PY) • between 0 and infinity

  29. Incidence Density Rate (IDR) calculation a /(t 1) = IDR outcome in expose c /(t 2) = IDR outcome in non expose

  30. PERSON-TIME CONCEPT • Documents/ASIALINK/life table.doc

  31. Incidence Density Rate (IDR) calculation a /(t 1) = IDR relaps in non radiotherapy ? c /(t 2) = IDR relaps in radiotherapy ?

  32. RESULT After 35 weeks follow up, we have 9 events of new cell growth in Ca cerviks stage 2 with radiotherapy out of 359 person-week, giving an incidence rate of new cell growth in patient Ca cervix stage 2 with radiotherapy is : • 9 / 359 = 0.025 • 9 cases / 359 person-weeks = • 25 cases / 1000 person in 35 weeks or • 37 cases / 1000 person in a year

  33. RESULT After 35 weeks follow up, we have 21 events of new cell growth in Ca cerviks stage 2 without having radiotherapy out of 182 person-week, giving an incidence rate of new cell growth in patient Ca cerviks stage 2 without having radiotherapy is • 21 / 182 = 0.115 • 21 cases / 182 person-weeks = • 115 cases / 1000 person in 35 weeks or • 172 cases / 1000 person in a year

  34. INSIDENCE DAN PREVALENCE 2004 2002 2003

  35. HUBUNGAN NILAI P = I x d Insidens Prevalens

  36. Exercise 1

  37. Exercise 1 Ad question 1: tonsillitis • Dutch population • 1 year • incidence • 19/1000 or 1.9%

  38. Exercise 1 Ad question 2: asthma • Children in the general practice • Certain moment (look into practice data at a certain moment) • Prevalence

  39. Exercise 1 Ad question 3: breast cancer • Women • Life • Incidence

  40. Exercise 1 Ad question 4: vertebral collapse • 9% • 55-59 year-old men and women • Certain moment • Prevalence

  41. Exercise 1 Ad question 5: fractures • Post-menopausal women • Follow-up duration of the study • Incidence

  42. Frequency measures: Incidence • How do we calculate a cumulative incidence?

  43. Frequency measures: example cohort • 13 persons followed for 5 years for mortality • A-----------------------------x--Moves away • B-----------------------------x-------------Death • C-------breast cancer/death • D-----------------------------x------------------------------------------- alive • E-----------------------------x--------lost to follow-up • F-----------------------------x--------------------------------------------alive • G-----------------------------x---------------------------breast cancer/death • H-----------------------------x-Myocardial infarction/death • I--------death • J------------------------------x-------------------------------------------alive • K-------------lost to follow-up • L-----------------------------x----------------moves from the area • M--------1---------------2--x----------3---------------4-------------------alive

  44. Frequency measures: example cohort • CI = 5/13 = 38% • Incidence density ?

  45. Frequency measures:Etiologic research • Suppose: you see a patient with lung cancer, who asks for the possible cause • Research question?

  46. Frequency measures:Etiologic research • Suppose: you see a patient with lung cancer, who asks for the possible cause • Research question: Is smoking a risk factor for lung cancer?

  47. Measures of association • Epidemiology • Disease = f (determinants) • Is the determinant associated with the disease? • Is the probability of disease different for exposed and non-exposed Ratio risk : Outcome risk in exposed Outcome risk in non exposed CIR ratio or IDR ratio

  48. Measures of association:Cohort approach • Research question? Is smoking associated with lung cancer? • Cohort approach • divide the cohort in smokers and non-smokers • estimate the incidence density (or CI) in each group • prior: ID smokers > ID not smokers

  49. Association measurement • RELATIVE RISK (RR) = Outcome incidence in expose group Outcome incidence in non expose group • RISK RATIO  (CIR ratio) • RATE RATIO (IDR ratio)

  50. (CIR) a /(a +b) Risk Ratio = c /(c +d)

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