epidemiology

• Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems
• It is the study of health and disease in the community
• Epidemiology seeks to relate disease to the population in which it occurs, including both sick and healthy
• Epidemiology is primarily concerned with population groups rather than individuals
• Early studies in epidemiology were concerned with the causes (aetiology) of communicable diseases
• Epidemiology is a basic medical science with the goal of improving the health of populations
• Cholera Case Fatality Rate

  Calculated as (Number of deaths / Number of cases) x 100
• Disease, illness and ill-health are not randomly distributed in a population
• Causation


  Cause of some diseases is genetic (e.g. phenylketonuria - PKU)
• Most common diseases result from an interaction between genetic and environmental factors
• Environmental factors affecting health

  • Biological
  • Chemical
  • Physical
  • Psychological
  • Other factors
• Behaviour + lifestyle epidemiology

  Used to study their influence + preventive intervention through health promotion
• Education & socioeconomic status are key factors in health
• Natural History


  The cause + outcome of diseases in individuals + groups
• Knowledge of the disease burden in populations is essential for health authorities
• Evaluation of intervention includes determining the appropriate length of stay in hospital for specific conditions
• Epidemiology shows correlation but not causation
• Correlation does not imply causation
• Risk ratio of 0.84 indicates a true reduction in colorectal cancer risk
• Risk ratio of 0.96 indicates not a true reduction in colorectal cancer risk
• Difficulty in determining whether observed associations are causal
• Epidemiology data can be easily misused + over-interpreted
• Determinants of disease include Agent, Host, Environment
• Epidemiology has direct relevance to human health, but it may be difficult in determining whether observed associations are causal
• Care needs to be taken when defining populations of study, otherwise results of study will be useless
• Epidemiology


  The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems
• Definition of Epidemiology
• Target Population/Population at Risk

  A defined group – sick or healthy, about whose health some statement is to be made
• Study Sample


  Must have an unambiguous definition of who is eligible
• Types of Epidemiological Studies

  • Descriptive studies
  • Analytical studies
• Descriptive Studies


  • Hypothesis generating
  • Study pattern of diseases within/between populations
  • Frequency + distribution of disease in relation to different variables
  • Can give clues/directions to cause + determinants of disease
• Analytical Studies


  • Hypotheses Testing
• Study Design


  1. Depends on the question being asked

  2. Population under investigation

  3. Resources available

  4. Time available
• Magnitude


  How big of a problem is a particular disease or condition?
• Time


  Is the incidence or prevalence of a particular condition increasing or decreasing over time?
• This seeming paradox results from there being twice as many women as men in this age group of this population
• Place


  How does incidence or prevalence vary from one area to another?
• You always want to know the size of the population any events occur in
• Persons


  Which people are most or least affected by the condition?
• NB: Epidemiological data gives an altered perspective to purely clinical data