Public Health Notes
Public Health Notes: Key Epidemiological Measures of Morbidity, Mortality, and Risk
Quick revision for BPH/MPH students and Loksewa candidates: Incidence rate vs Attack rate, Case Fatality Rate, Relative Risk, Odds Ratio, and Confounding control.
Public Health Concern Nepal Academic Cell · 7 min read
High-Yield Public Health Formulas
1. Incidence Rate vs Prevalence
- Incidence Rate: (Number of NEW cases occurring in a specified time period / Total person-time at risk) × 10^n
- Prevalence (Point/Period): (Number of ALL existing cases at a point in time / Total population at risk) × 100
- Prevalence Formula: $P = I \times D$ (where $I$ = Incidence and $D$ = Average Duration of disease)
2. Risk Estimation in Cohort vs Case-Control Studies
- Relative Risk (RR): Ratio of the incidence of disease among exposed to the incidence among unexposed ($RR = [a/(a+b)] / [c/(c+d)]$). Used strictly in Cohort Studies.
- Odds Ratio (OR): Cross-product ratio ($OR = (a \times d) / (b \times c)$). Used in Case-Control Studies as an approximation of Relative Risk when disease is rare.
3. Diagnostic Test Accuracy
- Sensitivity: Probability that a test detects disease when present ($a / [a+c]$)
- Specificity: Probability that a test is negative when disease is absent ($d / [b+d]$)
- Positive Predictive Value (PPV): Probability that a person has the disease given a positive test ($a / [a+b]$)