BIOSTATS LAB INTRODUCTION TO EPIDEMIOLOGY

• Epidemiology


  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
• Epidemiology


  • Studies conducted among human populations
  • Focuses on both sick and well people
  • Crucial difference is between those with the disease and those who are disease-free
• What epidemiologists study


  • Disease occurrence
  • Disease cause
  • Factor increasing risk of disease
  • Disease extent in a population
  • Natural history of disease
  • Disease characteristics
  • Preventive measures and policy decisions
• Epidemiologic terms


  • Distribution (Who has the problem?)
  • Determinants (What influences the problem?)
  • Risk factors (What characteristics are associated with the disease?)
  • Non-modifiable
  • Modifiable
• Issues addressed by epidemiology


  • Disease
  • Mortality
  • Hospitalization
  • Disability
  • Quality of life
  • Health status
• What does epidemiology do?


  1. Weighs and balances

  2. Contrasts and compares

  3. Use rates
• Leading Causes of Death, USA, 2000


  • Heart disease
  • Neoplasms
  • Cerebrovascular disease
  • Chronic pulmonary disease
  • Accidents/Injuries
  • Diabetes mellitus
  • Influenza and pneumonia
  • Alzheimer's disease
  • Nephritis, nephrotic syndrome
  • Septicemia
• Leading Causes of Death, Worldwide, 2000


  • Ischemic heart disease
  • Cerebrovascular disease
  • Lower respiratory infections
  • HIV/AIDS
  • COPD
  • Perinatal conditions
  • Diarrheal diseases
  • Tuberculosis
  • Road traffic injuries
  • Lung cancers
• Epidemiology rates

  • Events (numerator) - Number of people to whom something happened (i.e. they got sick, died, etc.)
  • Population at risk (denominator) - All the people at risk for the event
• Causes of epidemic


  • New agent
  • Change in existing agent (infectivity, pathogenicity, virulence)
  • Change in number of susceptible (population)
  • Environmental changes affecting transmission or growth of agent
• Epidemiologic triangle


  • Agent
  • Environment
  • Individual as a function of time
• The epidemiologic triangle - Agent


  • Infectious - microbes (bacteria, viruses)
  • Non-infectious - risk factors (smoking, high BP, exposure to chemicals/radiation)
• The epidemiologic triangle - Agent


  • Primary agent responsible or ascertain causative factors
  • Characteristics of the agent or causative factors
  • Mode of transmission
  • Contributing factors
  • Geographic patterns
• The epidemiologic triangle - Host


  • Organisms (humans, animals) exposed to and harbor a disease
  • Factors affecting susceptibility to disease - Age, gender, Race/ethnicity, Occupation, Immune status, Behaviors
• The epidemiologic triangle - Environment


  • Characteristics that may cause disease - Weather, Population density, Geography, Season of the year, Genetic effects / family history
• The epidemiologic triangle - Time


  • Duration when a person is sick, before death or recovery
  • Incubation period - time from infection to symptom development
  • Latency period - time from exposure to symptom development (chronic disease)
• Mission of epidemiology


  To study 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
• Demography


  The mathematical and statistical study of the size, composition and spatial distribution of human populations, and how these characteristics change over time
• Demographic processes

  • Fertility
  • Mortality
  • Migration
  • Marriage
  • Social mobility
• Uses of demography

  • Describing population composition
  • Analyzing population changes over time
  • Projecting future population trends
• Sex Ratio


  Compares the number of males to the number of females in a population
• Median Age


  The value which cuts-off the upper 50% and lower 50% of the ages of the population, used to gauge whether the population is young or old
• Age-Dependency Ratio


  Represents the number of dependents (young and old) that need to be supported by every 100 persons in the economically-active groups
• Population Pyramid


  • A graphical presentation of the age and sex composition of the population
  • Describes demographic trends of the population in the past
• The population pyramid can show demographic trends by the shape and structure of the age-sex distribution
• Epidemics happen when agent, environment, and individual as a function of time, are not in balance.
• A population pyramid presents the age and sex composition of the population and can show demographic trends.