Module 1

Cards (285)

  • GATE
    A Graphic Approach To Epidemiology
  • GATE uses a triangle, circle, square and arrows to graphically represent the design of all epidemiological studies, including experimental (mainly randomised trials) and non-experimental (i.e. observational) studies
  • Every epidemiological study can be hung on the GATE frame, which was developed so users could visualise key epidemiological principles, study design features, and analytical and appraisal concepts
  • GATE illustrates how every epidemiological study shares the same basic structure and how every epidemiological study is designed with the same objective - to measure how much dis-ease occurs in different groups (or populations)
  • Dis-ease
    Any health-related 'event' (e.g. an injury, a heart attack, a death) or health-related 'state' (e.g. diabetes, a disability, a raised blood pressure, or quality of life)
  • Epidemiologists generally study negative events or states, like death and disease, because they are easier to measure than positive states of health such as degrees of wellbeing
  • Occurrence (of dis-ease)

    The transition from a 'non-dis-eased state' to a 'dis-eased state'
  • Population
    Any group of people who share a specified common factor
  • Categorical data

    Data grouped into categories (e.g. male/female, smokers/ non-smokers, dead/alive)
  • Numerical data
    Data that take on numerical values (e.g. body weight, blood cholesterol levels, number of hospital visits)
  • Measuring dis-ease occurrence in a population can inform health service planners about types of health services required for populations, including health promotion, dis-ease prevention, disease diagnosis and treatment
  • Measuring dis-ease occurrence in different groups (e.g. smokers / non-smokers or Māori / non-Māori) in a population can identify risk factors, predictors & causes of dis-ease occurrence
  • Measuring dis-ease occurrence in groups treated with, say, different drugs or surgical interventions can help determine which treatments work best
  • Numerator
    The number of people in whom dis-ease occurs
  • Denominator
    The number of people in the study population
  • A key requirement of epidemiological studies is that the dis-ease outcomes counted (numerator) must all come from a defined population (denominator)
  • Epidemiology is the study of the occurrence of dis-ease in populations
  • GATE frame

    Illustrates the component parts of all epidemiological studies: the triangle represents the Participant (or Study) Population, the circle represents the study-specific sub-Denominators (Groups), the square represents the Numerators (or Dis-ease Outcomes), and the arrows represent Time
  • Exposure Group Occurrence (EGO)
    The occurrence of dis-ease in the Exposure Group
  • Comparison Group Occurrence (CGO)
    The occurrence of dis-ease in the Comparison Group
  • Numerical measures are often converted into categorical measures
  • When numerical outcomes are not converted into categories, the average or mean outcome can be calculated in each group
  • Incidence
    A measure of the occurrence of new cases of dis-ease in a population over a specified period of time
  • Prevalence
    A measure of the proportion of a population that has a dis-ease at a given point in time
  • Comparison group (CG)
    The group with low salt intake
  • Ideal study using categorical data
    • Everyone in P (the triangle) would also be in either EG or CG (the circle)
    • Everyone would be classified as either having a dis-ease outcome (a or b) or not having dis-ease (c or d) (the square)
    • The number of people in P should equal the number of people in EG & CG
    • The number of people in EG should equal the number of people in a & c
    • The number of people in CG should equal the number of people in b & d
  • Numerical exposure measures
    Salt intake classified numerically
  • Numerical outcome measure
    Blood pressure levels
  • Correlation coefficient
    Measure of the association between numerical exposures and numerical outcomes
  • Incidence
    Counting the number of onsets of dis-ease (events) occurring during a period of time
  • Prevalence
    Counting the number of people with dis-ease at a point of time
  • Incidence is the most appropriate measure for dis-eases with an easily observable onset

    e.g. number of hospital admissions for heart attacks over 5 years in smokers vs non-smokers
  • Incidence measures require the dis-ease outcome to be a categorical (e.g. yes / no) variable
  • Incidence Proportion (Risk)

    Counts everyone who started the study in the denominator and everyone who has a dis-ease onset during the study time period in the numerator
  • Incidence Rate
    A more exact measure of incidence, where once a person has an event, they are removed from the denominator. Participants are counted in units of person-time.
  • Unless the study has very long follow-up, high loss to follow-up, or high event rate, there will be little difference between Incidence Rate and Incidence Proportion
  • Incidence is typically calculated separately in the Exposure and Comparison Groups
  • Incidence measures always include a unit of time in the description
  • Prevalence
    Counting the number of people with dis-ease at a point of time (Numerator) and dividing by the number of people in the study group at that point in time (Denominator)
  • Prevalence is the measure used when the transition from non-dis-ease to dis-ease state cannot easily be observed and counted

    e.g. diabetes, raised blood pressure, overweight