1 / 96

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

lucas-marsh
Download Presentation

Frequency and Measures of Association

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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)

More Related