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WARM-UP

WARM-UP. Cohort Study. Kaijuan Wang 2008.11 . Cohort Study. Wenjie Yang ywjie@zzu.edu.cn 2004.12. Hypothesis. Analytical Epidemiology. Judging Causality. Prevention Strategies. Concept Map. Descriptive Epidemiology. Cross-Sectional Survey. Cohort Study. Case-control study.

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WARM-UP

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  1. WARM-UP

  2. Cohort Study Kaijuan Wang 2008.11

  3. Cohort Study Wenjie Yang ywjie@zzu.edu.cn 2004.12

  4. Hypothesis Analytical Epidemiology Judging Causality Prevention Strategies Concept Map Descriptive Epidemiology Cross-Sectional Survey Cohort Study Case-control study Experimental Epidemiology

  5. Cohort Study ★Postulate of Cohort Study ★Designing of Cohort Study ★Analysis of Cohort Study

  6. ★Postulate of Cohort study Definition of cohort Cohort: A group of people who share a common experience or condition. e.g. A cohort of smoker; A cohort of drug addict A cohort of A type behavior

  7. Cohort study:people who are free of disease are classified into two (or more) groups according to whether they are expose to a suspected factor or not(or different levels of the exposure) , and are followed over a period of time, the association between exposure and disease is evaluated by the difference of incidence rates of the two(or more) groups.

  8. smokers Lung cancer diseased Ie= exposed Follow-up diseased I0= Unexposed

  9. Types of cohort studyProspective Cohort Study Retrospective Cohort Study Ambispective Cohort Study

  10. Prospective Cohort Study diseased exposed nondiseased Initiation of study d unexposed nd now future

  11. Retrospective Cohort Study diseased exposed nondiseased Initiation of Study last d now unexposed nd

  12. Ambispective Cohort Study diseased exposed nondiseased Initiation of Study d now unexposed future nd Last

  13. Comparison Prospective cohort study Retrospective cohort study surveyed personally collected from historical records higher authenticity lower authenticity time-consuming time-saving expensive economic .

  14. ★ Design of cohort study 1 Ascertain the research goal 2 Define the exposure and fix on the measure method 3 Ascertain the research type 4 Ascertaina proper sample size

  15. A cohort study is to conducted to reveal the association between X-ray and leukaemia.We have know that: 1. the incidence rate of leukaemia in general population is 1 per 10 thousand approximately; 2. the incidence rate of leukaemia in X-ray exposed population is10 per 10 thousand approximately; Required:α=0.05 β=0.10 (Zα =1.96 Z β=1.28) An example

  16. P1 =0.0001, Q1=1-0.0001=0.9999 P2 =0.001, Q2=1-0.001=0.999 N=14247

  17. 5 Select research subject 5.1 Select the exposed group (1) From particular group A population that have a high level of exposure.

  18. ionic radiation leukemia radiologist uranium miner Atomic-bomb survivor

  19. 1) exposure is rare in general population,but relates to particular occupations , locations,life styles or experiences. 2) less time and less expense needed

  20. (2) From general population: 1) Exposure is relatively common . E.g. Smoking Tea drinking 2) Interested in the effect of moderate or low level of exposure

  21. 5.2 Selection of the comparison group Principle: Comparison group do not have exposure and should be as similar as possible with the exposed group except for the exposure .

  22. (1) internal comparison exposed inhomogeneous unexposed

  23. (2)external comparison exposed exposed Sampling inhomogeneous unexposed

  24. 6 Screen the subjects and collect the baseline data Screening of the subjects: exclude the subjects who have had the disease of interest collection of the baseline data: The exposure status Other risk factor status

  25. (1) Beginning of follow-up Latency period: the period between the initiation of exposure and the ascertainment of outcome (disease of interest) 7 Follow-up

  26. (2) Period of follow-up Depend on Strength of the association between exposure and disease

  27. (3)interval of follow-up Depend on stability of exposure status and the span of minimum latency period and maximum latency period

  28. (4) Task of follow-up exposure status outcome other risk factor exposure status

  29. (5) Main Methods of follow-up : ① Utilize varied routine record ② family interview ③ telephone or correspond inquiry

  30. ★Analysis of Cohort Study • 1 Measures of disease frequency (1) In fixed cohort(the status of participants is changeless) CI(cumulative incidence): The proportion of individuals who become diseased during a specified time period.

  31. number of new cases of a disease during the follow-up period CI= number of participants at the initiation of follow-up

  32. In a study of oral contraceptive use and bacteriauria, a total of 2400 women aged from 16 to 49 years were identified who were free from bacteriauria. Of these, 400 were OC users at the initiation. 3 years later,20 of the OC users had developed bacteriauria. • 3-year period CI=20/400=5.0%

  33. (2) in dynamic population(the status of participants is protean) ID(incidence density) :when the denominator is sum of person-time at risk, the incidence rate is called as ~.

  34. number of new cases of a disease during the follow-up period ID= total person-time of observation

  35. Jan, July, Jan, July Jan, July, Jan, July person 1998 1998 1999 1999 2000 2000 2001 2001 time A 2 B 2.5 C 2 D 3.5 Total person-time 10

  36. Exposed population General population Unexposed population

  37. Measures of association 1 RR (Relative Risk) ratio of the risk (i.e., incidence rate) in an exposed population to the risk in an unexposed, but otherwise similar, population. Incidence（exposed） RR= Incidence（unexposed）

  38. indicator of the strength (biological significance) of an association between an expose and disease.

  39. RR>1 Research factor is a risk factor (Positive association) RR<1 Research factor is a protective factor (Negative association ) RR=1 No association between the factor and the disease. Incidence（exposed） RR= Incidence（unexposed）

  40. strength no low middle high More higher

  41. For example, a relative risk of 2 associated with a risk factor means that persons with that risk factor have a doubled risk of having a specified outcome compared to persons without that risk factor.

  42. BreastNo Breast Cancer Cancer Total Alcohol 702,930 3,000 No alcohol 502,950 3,000 50 / 3,000 RR using Cumulative Incidence (CI): 70 / 3,000 RR = 1.4 =

  43. Smoking population Infinite population samples Non-smoking population

  44. Statistics: p-value indicates the likelihood that a study’s findings are due to chance in data analysis, RR =2.6, p=0.001 0.1% probability that the observed RR was a chance finding

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