Introductory workshop on Epidemiology Sep. 18 2024

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Points

  1. Types of epidemiological studies

    Observational studies

    • Ecological study

      • Information about groups of people
      • quick and easy
      • only correlations, may not be causal association
      • Hypothesis generating

    • Cross-sectional study

      • Uses individual data
      • Exposure and outcome assessed at the same time point
      • The comparison of disease frequency is based on prevalence of disease
      • Often used when it would be too complicated or too expensive to conduct a cohort or case-control study
      • Limited possibilities to infer causality since the exposure does not precede the outcome

    • Cohort study

      • An observational study where a defined group of people (the cohort) are followed over time, usually several years
      • Exposure measured at study start (before disease has occurred)
      • After/during the follow-up period, the incidence of the outcome (disease) is compared between exposed and unexposed
      • Suitable for rare exposure – use a highly exposed cohort
      • Time consuming, Large number of participants(expensive), Ineffective for rare diseases

    • Case-control study

      • Starts by identifying cases in a population
      • Randomly selected controls (free from the disease) are selected from the same population
      • Exposure assessed in cases and controls (i.e. retrospectively)
      • The occurrence (odds) of exposure is compared between cases and controls
      • Cost and time effective, Especially with rare diseases
      • Can investigate several exposures for one disease
      • Ineffective for rare exposures

    Intervention studies

    • Randomized controlled trails (RTC)

  2. Prevalence
    $$
    P = \frac{No. of\ persons\ with\ the\ disease\ at\ one\ point\ in\ time}{No.\ of\ persons\ in\ the\ defined\ population\ at\ the\ same\ time\ point}
    $$

  3. cumulative incidence (CI)
    $$
    CI = \frac{No.\ of\ new\ cases\ arising\ in\ the\ population\ over\ a\ given\ period\ of\ time}{No.\ of\ disease-free\ persons\ at\ the\ beginning\ of\ the\ time\ period}
    $$

  4. incidence rate (IR)
    $$
    IR = \frac{Number\ of\ new\ cases\ in\ a\ population\ over\ a\ given\ time\ period}{Total\ person-time\ at\ risk\ during\ that\ period}
    $$

  5. Two types of errors

    • Systematic errors
      • Selection bias
      • Information bias
        • Misclassification of exposure or outcome
      • Confounding
    • Random errors/errors of precision