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Spring , 2008

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  1. Spring , 2008 • STAT 6395 • Special Topic in Statistics: • Epidemiology Filardo and Ng, 2008

  2. I. Epidemiology The study of the distribution and determinants of health-related states or events in specified populations and the translation of study results to control health problems

  3. Persons affected Place Time Distribution Epidemiology: The study of the distribution and determinants of health-related states or events in specified populations and the translation of study results to control of health problems

  4. Determinants All the physical, biological, social, cultural, and behavioral factors that influence health Epidemiology: The study of the distribution and determinants of health-related states or events in specified populations and the translation of study results to control of health problems

  5. Health-related states or events • Diseases • Mortality (death) • Specific causes of death • Injuries • Disability • Health-related behaviors • Physiological measurements • Results of preventive regimens • Clinical outcomes • Provision and use of health services Epidemiology: The study of the distribution and determinants of health-related states or events in specified populations and the translation of study results to control of health problems

  6. Specified populations • Residents of a defined geographic area • Students who attend a specified school • Persons who belong to a specified organization • Workers at a specified workplace Epidemiology: The study of the distribution and determinants of health-related states or events in specified populations and the translation of study results to control of health problems

  7. Translation Study Results Scientific articles and presentations at meetings Clinical guidelines Prevention programs Quality of care improvement programs Patient safety programs Epidemiology: The study of the distribution and determinants of health-related states or events in specified populations and the translation of study results to control of health problems

  8. Control Operations or programs aimed at reducing the adverse impact of the disease on the community • Prevention • Cure • Management Epidemiology: The study of the distribution and determinants of health-related states or events in specified populations and the translation of study results to control of health problems

  9. Primary prevention An action taken to prevent the development of a disease in a person who is well and does not have the disease in question Operations or programs aimed at reducing the adverse impact of the disease on the community: 1) Prevention; 2) Cure; 3) Management

  10. Secondary prevention (Cure and management) The identification and treatment of people who have already developed a disease or precursors of the disease, through screening, at an early enough stage in the disease’s natural history (early detection) such that intervention will be more effective than if the disease had been discovered later Operations or programs aimed at reducing the adverse impact of the disease on the community: 1) Prevention; 2) Cure; 3) Management

  11. II. Objectives of Epidemiology • To describe the extent of disease in the community • To identify risk factors (factors that influence a person’s risk of acquiring a disease) for disease and the etiology or cause of disease • To study the natural history (course from onset to resolution) and prognosis of disease • To evaluate both existing and new preventive and therapeutic measures (including health care delivery) • To provide the foundation for developing public policy and regulatory decisions relating to environmental problems

  12. …bottom line, Epidemiology research requires a multidisciplinary effort and statisticians play a key role in: • Hypothesis development • Study execution

  13. Hypothesis development Epidemiologists study the specific distribution and determinants of specific diseases Development of hypotheses to test in an epidemiologic study requires in-depth knowledge of the disease and determinants under study • Medical and biological sciences • Social and behavioral sciences Epidemiology Research hypothesis development and study execution

  14. Study execution • Statistics ------------>Biostatistics • Medical and biological sciences • Social and behavioral sciences Epidemiology Research hypothesis development and study execution

  15. Biostatistics • Separate chance observations from meaningful observations • Sampling • Sophisticated statistical analyses Epidemiology Research Biostatistics, medical and biological sciences, social and behavioral sciences

  16. Medical and biological sciences • Microbiology, e.g., to identify infectious agents • Clinical medicine and pathology, (e.g., to identify cases of disease) • Molecular biology, (e.g., to identify genotype of individuals) • Biochemistry, (e.g., to measure serum hormone levels) Epidemiology Research Biostatistics, medical and biological sciences, social and behavioral sciences

  17. Social and behavioral science • Design questionnaires for obtaining valid information • Design effective interventions for lifestyle changes Epidemiology Research Biostatistics, medical and biological sciences, socialand behavioral sciences

  18. Epidemiology Sub-disciplines • Disease-specific subject matter • Exposure-specific subject matter • Health services research

  19. Disease-specific subject matter • Infectious disease epidemiology • HIV/AIDS epidemiology • Malaria epidemiology • Chronic disease epidemiology • Cancer epidemiology • Cardiovascular epidemiology • Perinatal epidemiology • Neuroepidemiology • Psychiatric epidemiology Epidemiology disciplines Disease-specific subject matter, Exposure-specific subject matter, Health services research

  20. Determinant (exposure)-specific subject matter • Environmental epidemiology • Occupational epidemiology • Pyschosocial epidemiology • Genetic epidemiology • Nutritional epidemiology • Pharmacoepidemiology Epidemiology disciplines Disease-specific subject matter, Exposure-specificsubject matter, Health services research

  21. Health services research • Operations research: the study of the placement of health services in the community and the optimum utilization of such services • Program evaluation • Clinical epidemiology or outcomes research: the study of illness outcomes in persons seen by providers of health care; evaluation of medical treatments Epidemiology disciplines Disease-specific subject matter, Exposure-specific subject matter, Health services research

  22. Types of epidemiologic studies • Experimental • Observational (this course will focus on this second type of studies)

  23. Experimental Studies • Studies in which conditions are under the control of the investigator(s). • The investigators assigns subjects to different study groups. The effect of the treatment is determined by comparing the outcome of interest in these groups. Type of studies Experimental, Observational

  24. Experimental studies (examples) • Randomized clinical trial (unit of study is the individual) • Community trial (unit of study is the community) Type of studies Experimental, Observational

  25. Observational studies • Studies in which the investigators does not control conditions, but rather observe nature taking its course by gathering information, recording, classifying, counting, and analyzing the collected data. • Exposure and disease outcomes would have occurred whether or not the studies have been performed because there were no ‘a priori’ intervention(s) on the part of the investigators. Type of studies Experimental, Observational

  26. Observational studies (examples) • Descriptive • Analytic Type of studies Experimental, Observational

  27. Descriptive studies Studies aimed at describing the distribution of disease or other health-related variables with respect to person (age, gender, race, socioeconomic status), place (census tract, county, state, country, urban/rural), and time (season, year) Type of studies Experimental, Observational (descriptive)

  28. Descriptive studies • Often use routinely-collected data • Can define high-risk groups • Can be used for hypothesis generation, but generally not hypothesis testing Type of studies Experimental, Observational (descriptive)

  29. Analytic studies • Test specific etiologic hypotheses • To generate new etiologic hypotheses • To suggest mechanisms of causation • To generate preventive hypotheses • To suggest or identify potential methods for disease prevention In these studies, the epidemiologist observes the relationship between an exposure and a disease or other health outcome. Type of studies Experimental, Observational (analytic)

  30. Definition: Exposure A potential causal agent or characteristic, such as infectious agent, behavior, dietary factor, medication, medical treatment, genetic makeup, environmental agent, or physiologic state (e.g., serum level of a hormone or nutrient; blood pressure). An exposure may be harmful or beneficial Type of studies Observational  Analytic

  31. Types of analytic studies • Cohort studies • Case-control studies Type of studies Observational

  32. Cohort studies A study in which a group of persons exposed to a factor of interest and a group of persons not exposed are followed and compared with respect to the incidence rate of the disease or other condition of interest Time Type of studies Observational Cohort studies

  33. Cohort studies (study schema) Type of studies Observational Cohort studies

  34. Case-Control studies Studies in which a group of persons with a disease (cases) and a comparison group of persons without the disease (controls) are compared with respect to the history of past exposures to factors of interest Past Present Type of studies Observational Case-Control

  35. Case-Control studies (study schema) Type of studies Observational Case-Control

  36. Time

  37. Either descriptive or analytic studies • Cross-sectional studies • Ecologic studies Type of studies Observational

  38. Cross-sectional studies Studies of the distribution of exposures and/or disease in a defined population at one given point in time Type of studies Observational Cross-sectional

  39. Ecologic studies Studies of the association between exposures and disease in which the units of analysis are populations or groups of people, rather than individuals. This involves the assessment of the correlation of exposure rates and disease rates among different groups or populations. Causality, though??? Type of studies Observational Ecologic

  40. Types of Epidemiologic studies

  41. Example involving several types of study designs Ecologic study results Case-Control study results Cohort study results Randomized controlled trial results

  42. Which type of study is the ‘Gold Standard’ and/or more common/feasible? Experimental Efficacy Observational Effectiveness controlled setting (difficult to reproduce in real life) real life setting

  43. Focus of this course is on observational Epidemiologic research (research regarding the direct study of disease in human populations)

  44. Some triumphs of observational Epidemiology • Smoking causes lung cancer • Identification of cardiovascular disease risk factors • Characterization of how HIV spreads through a population • Identification of occupational hazards (e.g., asbestos)

  45. Three ‘Eras’ of Epidemiology • Sanitary (1800-1875) • Infectious disease (1875-1950) • Chronic disease (1950-present)

  46. Sanitary ‘Era’ (1800-1875) • Miasma theory of disease – poisoning by foul emanations (miasma) from the soil, water, and air. • Created national vital statistics systems: much valuable descriptive epidemiology • Demonstrated clustering of disease in slums and among the poor • Solutions – sewage systems, drainage, clean water supplies, garbage collection, decent housing • Incorrect miasma theory, but solutions were a major contribution to public health Lesson: prevention doesn’t necessarily require understanding of cause Sanitary, Infectious disease, Chronic disease

  47. Infectious disease ‘Era’ (1875-1950) • Germ theory: single microscopic agents relate one-to-one to specific diseases • Epidemiology took a back seat to laboratory science, although in the1920s-30s, the germ theory was broadened to accommodate the interactive roles of host (immune and nutritional status), environment, and agent in infectious disease • Other epidemiologic contributions: • Occupational exposures as causes of cancer • Specific vitamin deficiencies as causes of disease Sanitary, Infectious disease, Chronic disease