Epidemiology Fundamentals

  1. Prevalence - measure of existing disease, a proportion (percentage) and unitless, e.g. 42.5% of a population has HSV-1
  2. Incidence - measure of a new disease
    • Cumulative Incidence - Assumes entire population followed for entire follow-up period; a unitless proportion
    • Incidence Rate - People contribute person-time only when at risk and meet definition of source population; person-time unit
  3. Descriptive studies
    • Case Report
    • Case Series
    • Cross-sectional Studies
    • Ecological (correlational) Studies
  4. Analytical studies
    • Case-Control Studies
    • Cohort Studies (Prospective and Retrospective)
    • Randomized Controlled Trial
  5. Hierarchy of Evidence: Systematic Reviews/Meta Analyses > RCTs > Cohort Studies > Case Control Studies > Case Series > Case Reports
  6. Sensitivity - Ability of a test to correctly identify patients with a disease: True Positives / (True Positives + False Negatives)
  7. Specificity - Ability of a test to correctly identify patients without a disease: True Negatives / (True Negatives + False Positives)
  8. Positive Predictive Value - True Positives / (True Positives + False Positives)
  9. Negative Predictive Value - True Negatives / (True Negatives + False Negatives)