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  1. 1. DESCRIPTIVE EPIDEMIOLOGY for Public Health Professionals Part 2 Ian R.H. Rockett, PhD, MPH Department of Community Medicine West Virginia University School of Medicine Prepared under the auspices of the Southeast Public Health Training Center, University of North Carolina, Chapel Hill, 2005. irockett@hsc.wvu.edu
  3. 3. The Epidemiologic Triad HOST AGENT ENVIRONMENT
  4. 4. Factors involved in the Natural History of Disease Agent Vector Host Environment
  5. 5. Epidemiologic Triad applied to Injury
  6. 6. Levels of Prevention  Primary  Secondary  Tertiary
  7. 7. The Haddon Matrix Physical Sociocultural Factors Human Agent Environment Environment Factors or Phases Vehicle Preevent Event Postevent
  8. 8. Source: Ian R.H. Rockett. Injury and Violence: A Public Health Perspective. Population Bulletin 53(4); 1998: 18. Adapted from G.S Smith and H. Falk, Unintentional Injuries. American Journal of Preventive Medicine 3(5) Supplement; 1997:143-163.
  9. 9. Haddon Matrix (bombings) Fact or s Per son Physical Envir on. Social Envir on. (bomb / bomber) Phases Pr e-event Teach t o r ecognize suspicious per sons Wear Event (explosion & pr ot ect ive clot hes collapse Post event Vehicle/ Vect or Tr ain people in f ir st aid Det ect able No vehicle zones bom bs Reduce anim osit y Slow er act ing ex plosives St r engt hen nor m s f or r escue volunt eer s St r engt hen public healt h inf r ast r uct ur e ?? Shat t er pr oof glass Em er gency call boxes
  10. 10. The Wheel of Causation Social Environment Biological Environment Host (human) Genetic Core Physical Environment
  11. 11. Web of Causation -- de-emphasizes the disease agent and allows for multifactorial causes
  12. 12. Web of Causation applied to Myocardial Infarction
  13. 13. Wider Application of the Web Epidemiologic Triad (devised to enhance search for understanding communicable disease) Web of Causation (devised to address chronic disease – can also be applied to communicable disease)
  15. 15. Natural History of Disease/Injury and Related Data Sources Good Health Disease Onset Symptoms Screening Test Results Care Diagnosis Therapy Seeking HEALTH OUTCOMES Cure Control Disability Death Interviews SELECTED DATA SOURCES Medical Records Hospital/ED Records Death Certificates Medical Examiner
  16. 16. Mortality (Death) Records
  17. 17. Source: Leon Gordis, Epidemiology, 2d edition; Philadelphia, PA: Saunders, 2000: 50.
  18. 18. Uncertainty in Reported Cause of Death 1) 2) 3) 4) Michael Alderson (1988) identified four areas where uncertainties or inaccuracies can arise in reporting causes of death: incorrect diagnosis (last attending physician and/or autopsy) incorrect completion of death certificate inaccurate processing and publication of the mortality statistics invalid classification of diseases/injuries
  19. 19. Multiple Cause-of-Death Analysis
  20. 20. Distinguishing Natural from Other Causes of Death
  21. 21. Use of Medical Examiner and Coroner Records to supplement Death Certificate Data Need to rule out homicide, suicide or “accident” , i.e., unintentional injury, before a death can be validly attributed to natural causes. Homicide or SIDS?
  22. 22. Disease and Injury Mortality are only the Tip of the Iceberg
  23. 23. Morbidity Data Sources
  24. 24. General Sources of Morbidity Data 1. Disease reporting -- communicable diseases, cancer registries 2. Data accumulated as a by-product of insurance and prepaid medical care plans a. Group health and accident insurance b. Prepaid medical care plans c. State disability insurance plans d. Life insurance companies e. Hospital insurance plans f. Railroad Retirement Board 3. a. b. c. d. Tax-financed public assistance and medical care plans Public assistance, aid to the blind, aid to the disabled State or federal medical care plans Armed Forces Veterans Administration
  25. 25. General Sources of Morbidity Data continued. . . 4. Hospitals and clinics 5. Absenteeism records -- industry and schools 6. Pre-employment and periodic physical examinations in industry and schools 7. Case-finding programs 8. Selective service records 9. Morbidity surveys on population samples (e.g., National Health Survey, National Cancer Surveys) Source: Leon Gordis. Epidemiology. Third edition. Philadelphia, PA, 2004: 37.
  26. 26. ICD and ICD-CM  The International Statistical Classification of Diseases and Related Health Problems (ICD) can be used for coding and classifying mortality data from death certificates  The International Classification of Diseases Clinical Modification (ICD-CM) can be used to code and classify disease and injury morbidity data from inpatient and outpatient records
  27. 27. Dynamic Classification Causes of disease, injury and disability may wax and wane. ICD needs to be flexible, especially in responding to new circumstances: e.g. SARS, terrorism attributable health outcomes as from such varied causes as asphyxiation, chemical burns, falls and jumping from buildings, and suicide and suicide attempts
  28. 28. Primary data are new data collected by or for the investigator Secondary data refer to existing data
  29. 29. Stages of Development of Information 1) Public health surveillance – development and refinement of data systems for the ongoing and systematic collection, analysis, interpretation and dissemination of information
  30. 30. Stages of Development of Information 2) Risk group identification – identification of persons at greatest risk of disease or injury and the places, times, and other circumstances that are associated with elevated risks
  31. 31. Stages of Development of Information 3) Risk factor identification – analytic exploration of potentially causative risk factors for disease, injury or death as suggested by the high risk population and other research
  32. 32. Stages of Development of Information 4) Program development, implementation, and evaluation – design, implementation and evaluation of preventive interventions based on degree of understanding of the population-at-risk and the risk factors for the outcome of interest
  33. 33. A Caveat on Data Quality (“garbage in - garbage out”)
  34. 34. The government is very keen on amassing statistics. They collect them, add them, raise them to the nth power, take the cube root and prepare wonderful diagrams. But you must never forget that every one of these figures comes in the first instance from the village watchman, who just puts down what he damn well pleases. Sir Josiah Stamp, British Economist (1880-1941)