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Introduction To Epidemiology

Introduction To Epidemiology. Mr. Manuel. What is Epidemiology?. Definition of Epidemiology. Last JM: A Dictionary of Epidemiology

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Introduction To Epidemiology

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  1. Introduction To Epidemiology Mr. Manuel

  2. What is Epidemiology?

  3. Definition of Epidemiology Last JM: A Dictionary of Epidemiology The study of the distribution and determinants of health related states and events in populations and the application of this study to control of health problems

  4. What Is The Unique Skill Of Epidemiologists? Measuring disease frequency in populations

  5. Measuring Disease Frequency Has Several Components Classifying and categorizing disease Deciding what constitutes a case of disease in a study Finding a source for ascertaining the cases Defining the population at risk of disease Defining the period of time of risk of disease Obtaining permission to study people Making measurements of disease frequency Relating cases to population and time at risk

  6. Two Broad Types of Epidemiology Examining the distribution of a disease in a population, and observing the basic features of its distribution in terms of time, place, and person. Typical study design: community health survey (approximate synonyms - cross-sectional study, descriptive study) Testing a specific hypothesis about the relationship of a disease to a putative cause, by conducting an epidemiologic study that relates the exposure of interest to the disease of interest. Typical study designs: cohort, case-control DESCRIPTIVE EPIDEMIOLOGY ANALYTIC EPIDEMIOLOGY

  7. The Basic Triad Of Descriptive Epidemiology THE THREE ESSENTIAL CHARACTERISTICS OF DISEASE WE LOOK FOR IN DESCRIPTIVE EPIDEMIOLOGY ARE: PERSON PLACE TIME

  8. Person (characteristics?) Age Gender Socio-economic status (education, occupation, income) Marital status Ethnicity/race/genetic profile Behavior / habits

  9. Place (where ?) Geographically restricted or widespread (outbreak, epidemic, pandemic)? Off-shore (tsunami…) Climate effects (temperature, humidity, combined effects..) Urban / sub-urban-squatter / rural   Relation to environmental exposure (water, food supply, etc)   Multiple clusters or one?

  10. Time (when ?) Changing or stable? Clustered (epidemic) or evenly distributed (endemic)? Time-trends: Point source, propagated, seasonal, secular, combinations

  11. Data Collection Methods • Primary: where the investigator is the first to collect the data. Sources include: medical examinations, interviews, observations, etc. Pros: less measurement error, suits objectives of the study better. Cons: costly, may not be feasible. • Secondary: where the data is collected by OTHERS, for other purposes that those of the current study. Sources include: individual records (medical / employment); group records (census data, vital statistics)

  12. Descriptive Epidemiology Is A Necessary Antecedent Of Analytic Epidemiology To undertake an analytic epidemiologic study you must first: Know where to look Know what to control for Be able to formulate hypotheses compatible with laboratory evidence

  13. A common error in epidemiology is moving to analytic epidemiology without having a solid base in the descriptive epidemiology of the condition is useless.

  14. Epidemiologists are required to have some knowledge of the disciplines of the following: • public health, because of the emphasis on disease prevention. • clinical medicine, because of the emphasis on disease classification and diagnosis. 

  15. pathophysiology, because of the need to understand basic biological mechanisms in disease. • statistics, because of the need to quantify disease frequency and its relationships to antecedents. • social sciences, because of the need to understand the social context in which disease occurs and presents.

  16. Purposes Of Epidemiology Identify causes and risk factors for disease. Determine the extent of disease in the community. Study natural history and prognosis of disease. Evaluate preventive and therapeutic measures Provide foundation for public policy

  17. EVERY HEALTH OUTCOME HAS SOME INTERESTING AND USEFUL EPIDEMIOLOGIC CHARACTERISTIC DEATH RATES BY SOCIAL CLASS FROM A CERTAIN CAUSE AMONG 1,316 PEOPLE WHAT CAUSE OF DEATH IS THIS?

  18. The previous slide shows death rates by class of ticket on the Titanic, a large ocean liner that sank after colliding with an iceberg in 1912

  19. Pandemic Influenza Phases Time: Mondays and Wednesdays 4:10-5:20 p.m. Office hours: BY ARRANGEMENT Place: Room A -131 East Fee Hall Department of Epidemiology classroom. Person: Nigel Paneth, Instructor. 353-8623; paneth@msu.edu

  20. WHO phases of pandemic alert -Phase 4 • Verified human-to-human transmission of an animal or human-animal influenza reassortment virus able to cause “community-level outbreaks.” • The ability to cause sustained disease outbreaks in a community marks a significant upwards shift in the risk for a pandemic. • Indicates a significant increase in risk of a pandemic but does not necessarily mean that a pandemic is a forgone conclusion.

  21. Phase 5 • Human-to-human spread of the virus into at least two countries in one WHO region. While most countries will not be affected at this stage • Is a strong signal that a pandemic is imminent and that the time to finalize the organization, communication, and implementation of the planned mitigation measures is short.

  22. Phase 6 (pandemic phase) • Community level outbreaks in at least one other country in a different WHO region in addition to the criteria defined in Phase 5. • Indicate that a global pandemic is under way.

  23. Differences Between Laboratory Sciences And Field Sciences In the Field: Mostly observational  Variables controlled by nature  Some variables unknown  Replication difficult; exact replication impossible  Results often uncertain  Meaning of results for humans clear  Statistical control often very important  Highly labor intensive

  24. Differences Between Laboratory Sciences And Field Sciences In the Laboratory: Mostly experimental Variables controlled by the investigator All variables known Replication easy Results valid Meaning of results for humans uncertain. Little need for statistical manipulation of data. Highly equipment intensive

  25. The Basic Triad Of Analytic Epidemiology THE THREE PHENOMENAASSESSED IN ANALYTIC EPIDEMIOLOGY ARE: HOST AGENT ENVIRONMENT

  26. Host Age Socio-economic status Gender Ethnicity/Race Behavior

  27. Agent Living/Non-living Species Behavior Habitat If the agent is human, gender, race etc. are factors Examples: Nutrients, Poisons, Allergens, Radiation, Physical trauma, Microbes, Psychological experiences

  28. Host Factors Genetic endowment Immunologic state Age Personal behavior

  29. Environment Crowding Atmosphere Modes of communication – phenomena in the environment that bring host and agent together, such as: Vector Vehicle Reservoir

  30. Environment Geographically restricted or widespread (pandemic)?   Relation to water or food supply.   Multiple clusters or one?

  31. Analytical Epidemiology

  32. Study Development Process Descriptive Studies: Data Collection and Analysis Model Building and hypothesis formulation Analyze results and retest Analytic Studies for Hypothesis testing

  33. Study Designs - Analytic Epidemiology • Experimental Studies • Randomized controlled clinical trials • Community trials • Observational Studies • Group data • Ecologic • Individual data • Cross-sectional • Cohort • Case-control

  34. Experimental Studies • treatment and exposures occur in a “controlled” environment • planned research designs • clinical trials are the most well known experimental design. Clinical trials use randomly assigned data. • Community trials use nonrandom data

  35. Observational Studies • non-experimental • observational because there is no individual intervention • treatment and exposures occur in a “non-controlled” environment • individuals can be observed prospectively, retrospectively, or currently

  36. Cross-sectional studies • An “observational” design that surveys exposures and disease status at a single point in time (a cross-section of the population) time Study only exists at this point in time

  37. Cross-sectional Studies • Often used to study conditions that are relatively frequent with long duration of expression (nonfatal, chronic conditions) • It measures prevalence, not incidence of disease • Example: community surveys • Not suitable for studying rare or highly fatal diseases or a disease with short duration of expression

  38. Cross-sectional Design factor present No Disease factor absent Study population factor present Disease factor absent time Study only exists at this point in time

  39. Epidemiologic Study Designs • Case-Control Studies • an “observational” design comparing exposures in disease cases vs. healthy controls from same population • exposure data collected retrospectively • most feasible design where disease outcomes are rare

  40. Case-Control Studies Cases: Disease Controls: No disease

  41. Case-Control Studies • Strengths • Less expensive and time consuming • Efficient for studying rare diseases • Limitations • Inappropriate when disease outcome for exposure is not known at start of study • Exposure measurements taken after disease occurrence • Disease status can influence selection of subjects

  42. Case-Control Design factor present Cases (disease) factor absent Study population factor present Controls (no disease) factor absent present past time Study begins here

  43. Epidemiologic Study Designs • Cohort Studies • an “observational” design comparing individuals with a known risk factor or exposure with others without the risk factor or exposure • looking for a difference in the risk (incidence) of a disease over time • best observational design • data usually collected prospectively (some retrospective)

  44. Cohort Design disease Factor present no disease Study population free of disease disease Factor absent no disease present future time Study begins here

  45. Timeframe of Studies • Prospective Study - looks forward, looks to the future, examines future events, follows a condition, concern or disease into the future time Study begins here

  46. Prospective Cohort study Exposed Outcome Measure exposure and confounder variables Non-exposed Outcome Baseline time Study begins here

  47. time Study begins here Timeframe of Studies • Retrospective Study - “to look back”, looks back in time to study events that have already occurred

  48. Retrospective Cohort study Exposed Outcome Measure exposure and confounder variables Non-exposed Outcome Baseline time Study begins here

  49. Cohort Study • Strengths • Exposure status determined before disease detection • Subjects selected before disease detection • Can study several outcomes for each exposure • Limitations • Expensive and time-consuming • Inefficient for rare diseases or diseases with long latency • Loss to follow-up

  50. Experimental Studies • investigator can “control” the exposure • akin to laboratory experiments except living populations are the subjects • generally involves random assignment to groups • clinical trials are the most well known experimental design • the ultimate step in testing causal hypotheses

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