Using Epidemiology to Identify the Cause of Disease: Cohort study

Transcription

1 Using Epidemiology to Identify the Cause of Disease: Cohort study Sakda Arj-ong Vallipakorn, M.D., MSICT., MSIS., PhD.(Clinical Epidemiology) Pediatrics, Pediatric Cardiology Emergency Medicine, Pediatric Emergency Medicine Ramathibodi Hospital, Mahidol University

2 What is the risk factor of disease Smoking CA Lung C-reactive protein Heart diseases

3 Assign exposure / intervention? yes no Experimental Observational Comparison group? yes no Analytic Descriptive Start with Outcome or Exposure E O E O E/O Case-control Cohort Cross sectional

4 Assign exposure / intervention? yes no Experimental Observational Comparison group? yes no Analytic Descriptive Start with Outcome or Exposure E O E O E/O Case-control Cohort Cross sectional

5 Cohort study cohort Group whose members share a significant experience at a certain period of time or have one or more similar characteristics. People born in the same year, for example, are the birth cohorts (generation) for that year. Similarly, married men or those who smoke are cohorts of the other married men or other smokers.

6 Bad Training Environment Burn out Residents Good Training Environment

7 Criteria for cohort study 1. Do not have the outcome at the time that study started 2. F/U time should be sufficient for the outcome to be expressed 3. Members of the cohort should be observed over the full period of F/U

8 Framingham study Begun in 1949 Identified factors associated with CHD 5,209 men and women, aged Study ran for 30 years Continues with Framingham Offspring study

9 Types of cohort study Prospective cohort study Retrospective cohort or historical cohort study

10 Past Present Future NO Dz Diseases Cohort assembled Prospective cohort Follow-up

11 Past Present Future Cohort assembled Rama Personal Retrospective cohort Follow-up Obesity Cohort assembled Prospective cohort CVD, Stroke Follow-up

12 Retrospective or historical cohort study

13 Present MMR MMR vaccine Mump Measles Rubella Non MMR vaccine

14 Advantage Temporal sequence Concurrent Exposure Outcome Rare exposure; occupational setting

15 Advantage Can assess the relationship between exposure and many diseases ( one : many) n 1 n Breast cancer melanoma n Ovarian Cancer

16 Disadvantages Cannot be used for rare disease

17 Disadvantage Long latency period Exposure Outcome Time consuming Expensive/Budget loss Loss F/U

18 Selection of exposed population Common or Rare exposure?

19 Selection of exposed population Common exposure & common disease ability to complete and accurate information

20 Source of information 1. Preexisting record 2. Interview, questionnaire 3. Direct physical exam 4. Laboratory

21 Source of outcome data 1. Death certificate 2. Periodic health examination 3. Physician record, hospital discharge

22 Loss to F/U How long? Exposure Outcome Time

23 Outpatient record Town s resident list Military records Employment records Small amount of Loss F/U Loss F/U equally between expose and non expose

24 Way to express and compare risk

25 Incidence rate or risk of developing disease

26 Develop disease Not develop disease Incidence Rate Exposed a b a a+b Non exposed c d c c+d

27 Developed lung CA Not developed Lung CA Incidence Rate Smoked Nonsmoked

28 Measures of effects in Cohort Study Risk difference Relative risk

29 Risk difference Incidence rate Expose incidnce rate Non-expose Incidence rate smoking incidnce rate Non-smoking

30 Developed lung CA Not developed Lung CA Incidence Rate Smoked Non-smoked Risk difference = = 0.09 = 9%

31 Relative risk The ratio of the incidence rate between exposed and non-exposed RR = incidence in exposed incidence in non-exposed

32 Developed lung CA Not developed Lung CA Incidence Rate Smoked Non-smoked Relative risk = 0.1/0.01= 10

33 Interpreting Relative Risk IR Ex = IR non RR = 1 (no association) IR Ex > IR non RR > 1 (risk effect) IR Ex < IR non RR < 1 (protective effect