1 / 68

Descriptive Epidemiology & Study design

Descriptive Epidemiology & Study design. Potjaman Siriarayapon Bureau of Epidemiology. Outline. General concept of descriptive epidemiology Study design in epidemiology Descriptive Analytic. Banluang district, Nan province.

wendi
Download Presentation

Descriptive Epidemiology & Study design

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. Descriptive Epidemiology & Study design Potjaman Siriarayapon Bureau of Epidemiology

  2. Outline • General concept of descriptive epidemiology • Study design in epidemiology • Descriptive • Analytic

  3. Banluang district, Nan province

  4. Average Rate of Cholangiocarcinoma among in-patients visiting Nan Hospital, by district, Nan province, 1997 - 2002 Source : ICD10 Nan Hospital

  5. Average Rate of Hepatocellular carcinoma among in-patients visiting Nan Hospital, by district, Nan province, 1997 - 2002 Source : ICD10 Nan Hospital

  6. How would to do to answer this problem?

  7. DEFINITION OF EPIDEMIOLOGY "Epidemiolgy is the study of the distribution and determinants of health-related states or events in specified populations and the application of this study to the control of health problems" (John M. Last, 1988)

  8. KEY CONCEPTS • “Descriptive epidemiology” is the first step in epidemiological study. Careful observation of available information alone have led many successful preventive measures in the past. Describing health or disease occurrence according to place, person and time can lead to very meaningful hypothesis formulations.

  9. TIME • Disease rates change over time. Some of these change occur regularly and can be predicted. • By examining events that precede a disease rate increase or decrease, we may identify causes and appropriate actions to control or prevent further occurrence of the disease.

  10. Influx of rat Secular (long-term) trends: to predict or evaluate control program Reported Cases of Leptospirosis per 100,000 Population, Thailand, 1990-1999.

  11. Seasonality:to see seasonal pattern over years Cases Cases of eosinophilic meningitis, Nan province, Thailand, 1997-1999 Onset by Month

  12. Day of week and time of day:especially important for condition that related to occupational or environmental condition Deaths Time of Day Fatalities associated with farm tractor injuries by time of day, Georgia, 1971-1981

  13. Flood Epidemic period:to show the time course of disease outbreak Cases Date of onset Number of leptospirosis patients by date of onset, Nov 25-Dec 21, 2000

  14. PLACE • We describe a health event by place to gain insight into the geographical extent of the problem. • We may use place of residence, birthplace, place of employment, school district, hospital unit, etc., depending on which may be related to the occurrence of the health event.

  15. village Meningococcal cases, Tak province, 2002-2003 Myanmar Umphang district Refugee camp Nov.-Dec. Jan-Feb. Mar.

  16. Thai-Myanmar border area in Umphang district

  17. In the refugee camp

  18. House of Karen people outside the camp

  19. PERSON • There are several person categories available: • inherent characteristics: age, sex, race • acquired characteristics: marital status, immune • activities: occupation, use of medication/tobacco/drugs • condition under which their live: socioeconomic status, access to medical care

  20. Sex specific attack rates of reported leptospirosis cases, Songkla, Nov 25-Dec 15, 2000

  21. Age specific attack rates of reported leptospirosis cases, Songkla, Nov 25-Dec 15, 2000

  22. Study design

  23. Why “type of study”? • Design more appropriate studies to get right answers to the specific questions • Getting more optional study design to the questions • Shape up proposals for getting more valid results

  24. Descriptive Little is known - Identify cases, estimate disease about the frequency, examine time trend Studies occurrence, or - Justify additional (analytic) determinants of the studies to test hypotheses disease Analytic Enough is known - Test specific etiologic hypotheses about the d disease, Studies - Justify additional studies specific hypotheses - Suggest potential for disease can be tested prevention TYPES OF OBSERVATIONAL STUDIES

  25. STUDY DESIGN OF DESCRIPTIVE STUDY

  26. STUDY DESIGN OF DESCRIPTIVE STUDY • Individual level • Case reports or case series • Cross-sectional surveys of individual • Population level • Ecological study (Correlational study)

  27. CASE REPORTS AND CASE SERIES • Case reports : describe experience of a single patients. Case reports document unusual medical occurrence and can represent the first clues in the identification of new diseases. • Case series : collections of individual case reports. Investigation of the activities of the individual in case reports can lead to formulation of a hypothesis.

  28. SARS situation

  29. CASE REPORTS AND CASE SERIES • Stength • discover new diseases • bring background information to form hypothesis about risk factors • Weakness • might base on only one case • do not have a comparison group

  30. CROSS-SECTIONAL STUDY Total population Cases

  31. Character of cross-sectional study • Collect data for all population; case & healthy people • Information obtain is the number of total cases at that study period: prevalence • Can be either descriptive or analytic, depend on design

  32. Descriptive Collected number of cases and number of total population Can assess only prevalence of disease or other health events, also called prevalence study Analytic Exposure and disease status are assessed simultaneously Can determine association between exposure and disease CROSS-SECTIONAL STUDY

  33. Vaccine coverage among Thai children • Proportion of children received vaccine • Education level of mother and vaccine status in children

  34. Exposed Have disease Cross-sectional study Defined Population Gather Data on Exposure and Disease Not exposed: Have disease Not Exposed: Do not have disease Exposed Do not have disease

  35. Hypothetical illustration of the interrelationship between an occupational exposure and prevalence of disease 80 well 80 well 100 Workers Job A (hazardous) 10 change jobs due to illness 20 ill 10 ill 95 well 95 well Job B (non-hazardous) 100 Workers 5 ill 10 ill 15 ill Point X Prevalence of job A = 20 % ( 20/100 ) Prevalence of job B = 5 % ( 5/100 ) Prevalence ratio = 4

  36. Hypothetical illustration of the interrelationship between an occupational exposure and prevalence of disease 80 well 80 well 100 Workers Job A (hazardous) 10 change jobs due to illness 20 ill 10 ill 95 well 95 well Job B (non-hazardous) 100 Workers 5 ill 10 ill 15 ill Point Y Prevalence of job A = 11 % ( 10/90 ) Prevalence of job B = 14 % ( 15/110 ) Prevalence ratio = 0.8

  37. PROBLEM OF CROSS-SECTIONAL STUDY • Difficult to establish temporal relationship • Can assess only association but not a “causal association” • Length biased sampling: Disease that has long duration will over-represent the magnitude of illness while short duration will under-represent illness.

  38. STUDY DESIGN OF DESCRIPTIVE STUDY • Individual level • Case reports or case series • Cross-sectional surveys of individual • Population level • Ecological study (Correlational study)

  39. ECOLOGICAL STUDY • These studies are an extension of the use of routine data. • Essentially the average exposure of the population is plotted against the rate of the outcome for that population • This is done for several populations and the data are then examined for evidence of an association between exposure and outcome.

  40. Study to find relationship between suicide rate and proportion of Protestant Group of Proportion of Suicide rate Prussian Province Protestant (per 100,000 pop.) A 9.56 0.30 B 16.36 0.45 C 22.00 0.79 D 26.46 0.95

  41. Suicide rate (per 10 5/year) Correlation between proportion of protestant and suicidal rate in 4 groups of Prussian provinces Prov. Proportion ofSuicide Protestantrate A 9.56 0.30 B 16.36 0.45 C 22.00 0.79 D 26.46 0.95 Proportion of Protestant

  42. Rationale for ecological study • Low cost and convenience: make use of existing data • Measurement limitations of individual-level studies: environmental study • Interest in ecological effect: social norm, population intervention

  43. ECOLOGICAL STUDY • Strength:cheap, quick and convenient since it usually come from existing data • Weakness: • inability to link exposure with disease in individual (ecological fallacy) • limit to control effect of other factors

  44. Ecological or correlation study • In summary • Ecological study is a convenient, cheap and simple study. • Unit of study is the aggregate data not individual level. • It is usually be conducted as the first step study for research. • The result is difficult to interpret because of confounding and bias.

  45. Summary of the study design

  46. Analytic study

  47. Exposed and NotExposed Cohort study Population at risk Disease among exposed? Disease among non-exposed? Usuallyprospective

  48. Risk a a+b c c+d Distribution of illness according to exposure in a cohort study Not ill Ill b a+b a Exposed Not exposed c d c+d Relative risk = Risk exposed / Risk not exposed

  49. Key features • Should have follow up period (even in retro-cohort) • Have confine population • Comparison group should be as similar as possible

More Related