Epidemiology Public Health

# Epi PH Overview

## 1. Core Principles
Epi is the study of distribution and determinants of health-related states in populations. 
- **Descriptive Epi**: Person, Place, Time (PPT).
- **Analytic Epi**: Testing hypotheses via observational studies (cohort, case-control) and experimental trials (RCTs).

## 2. Quantitative Metrics
- **Incidence vs Prevalence**: Incidence captures new cases (risk); Prevalence captures existing burden.
- **RR & OR**: RR used in cohort studies; OR used in case-control studies. 
- **DALY Calculation**: DALY = YLL + YLD. Essential for global health burden assessment.

## 3. Study Designs & Bias
- **Confounding**: A third variable distorting the relationship between exposure and outcome. Controlled via randomization, restriction, or matching.
- **Bias**: Selection bias (systematic error in subject selection) vs Information bias (measurement error).

## 4. Disease Transmission Dynamics
- **R0 (Basic Reproduction Number)**: Expected number of secondary cases produced by a single infection in a completely susceptible population.
- **Herd Immunity**: Threshold = 1 - (1/R0).

## 5. Public Health Application
- **Surveillance Systems**: Passive vs Active. 
- **Policy**: Translation of evidence into practice (EBP). Analysis of CI95% for statistical significance in policy decisions.