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Epidemiology: Risk Factors, Study Designs, and Prevention

Incidence, Prevalence, Morbidity, and Mortality

  • Incidence describes new cases in a population at risk over a period, reflecting how many new cases emerge over time.

  • Incidence rate captures the appearance of new cases within a defined population over a defined time interval.

  • Morbidity refers to the disease burden and disability. Mortality refers to death from the disease. They are related but do not always move together, and can vary geographically.

  • These terms are crucial for understanding disease burden and public health priorities.

Risk factors: genetic, congenital, acquired, and environment

  • Genetic risk factors are hereditary elements increasing disease risk.

  • Congenital risk factors are conditions present at birth; all genetic factors are congenital, but not all congenital factors are genetic.

  • Acquired risk factors develop after birth from environmental or behavioral exposures.

  • Non-modifiable risk factors cannot be changed (e.g., age, sex, height).

  • Modifiable risk factors can be changed (e.g., exercise, nutrition, smoking). Environmental risk modifiability is complex, involving both individual action and societal policy.

Data, study designs, and the role of risk-factor identification

  • Cross-sectional studies: Collect data at a single point in time to identify associations. Pros: time-efficient; Cons: cannot establish temporality or causation.

  • Cohort studies: Follow participants over time, collecting data regularly. Pros: can establish temporality and analyze incidence; powerful for identifying risk factors. Cons: expensive, complex, long-term.

  • Primary goal of studying risk factors: To prevent disease (primary prevention) or prevent risk factors from leading to disease progression.

Prevention framework: primary, secondary, and tertiary

  • Primary prevention: Prevents disease by reducing exposure to risk factors (e.g., reducing smoking, improving air quality).

  • Secondary prevention: Early detection and intervention to prevent disease progression and complications (e.g., hypertension screening).

  • Tertiary prevention: Manages established disease to slow progression, reduce morbidity, and minimize adverse outcomes (e.g., treating symptoms).

Connections, implications, and ethical considerations

  • Connects to public health principles: causation, temporality, confounding, association vs. causation.

  • Policy implications: Environmental regulations can have broad impacts, but face political/economic factors.

  • Individual vs. population-level outcomes: Individual actions (quitting smoking, masks) are important, but systemic changes are often needed for meaningful risk reduction.

  • Ethical considerations: Equity in exposure and access to interventions, protecting privacy in studies.

Key formulas and reference concepts (epidemiology basics)

  • Incidence rate (new cases per person-time): IR = \frac{I}{P \times t}

  • Cumulative incidence (risk over a period): CI = \frac{I}{N}

  • Prevalence (existing cases at a point in time): Prev = \frac{C}{N}

  • Morbidity rate: Measure of disease burden/disability.

  • Mortality rate: MR = \frac{D}{N}

  • Relative risk (risk in exposed vs unexposed): RR = \frac{P(\text{disease}|\text{exposed})}{P(\text{disease}|\text{unexposed})}

  • Odds ratio (odds of disease in exposed vs unexposed): OR = \frac{ \frac{P(\text{disease}|\text{exposed})}{1 - P(\text{disease}|\text{exposed})} }{ \frac{P(\text{disease}|\text{unexposed})}{1 - P(\text{disease}|\text{unexposed})} }