Epidemiological Methods: Studying Health and Disease in Populations

Posted on May 4, 2024 in Biology

Epidemiological Methods in the Health Status Study

Definition: Epidemiology is the study of the distribution of disease and determinants of health in populations. It examines health-related states and events, focusing on specific populations, and applies this knowledge to control health problems. (Last J. M., A Dictionary of Epidemiology, 1998)

Etymology

The term “epidemiology” has Greek roots:

  • Epi = upon, among
  • Demos = people, district
  • Logos = study

Goals of Epidemiology

Epidemiology aims to:

  • Study the distribution of health and disease
  • Identify determinants influencing health and disease distribution
  • Establish appropriate control measures
  • Assess the efficacy of chosen measures

Working Methods

Epidemiologists address both theoretical and practical questions:

  • Theoretical questions: Studying the epidemic process (chain of infection)
  • Practical questions: Defining plans for preventing and controlling infectious diseases

Theoretical Epidemiology

Descriptive Epidemiology

Descriptive epidemiology identifies and reports patterns and frequencies of health events within a population. It requires three types of data:

  1. Time:
    • Regular fluctuations (seasonal vs. periodic)
    • Irregular fluctuations (e.g., cholera, malaria, HIV, HAV)
    • Secular trends (e.g., TB)
  2. Place:
    • Population location (urban vs. rural), density
    • Migrations
    • Geographical features (soil type, climate, global location)
  3. Person: Age, sex, occupation, ethnicity, etc.

Analytical Epidemiology

Analytical epidemiology formulates hypotheses about disease causes and focuses on identifying determinants of health outcomes, seeking to explain the “why” and “how” behind health events.

Practical Epidemiology

Experimental Epidemiology

This involves interventions to assess the impact of measures, such as evaluating the efficacy of a new vaccine.

Prevention

Epidemiology plays a crucial role in disease prevention:

  • Primary prevention: Aims to prevent disease onset and control risk factors (e.g., vaccination, food security, disinfection)
  • Secondary prevention: Aims to prevent complications, disease progression, or recurrence
  • Tertiary prevention: Aims to reduce complications and progression of established diseases

Epidemiological Studies

Treatment Studies

  • Randomized controlled trials:
    • Double-blind, single-blind, and non-blind trials
  • Non-randomized controlled studies

Observational Studies

1. Longitudinal Studies

  • Cohort: A group of people sharing a common characteristic or experience within a defined period (e.g., birth year, exposure to a drug, vaccine, pollutant, or medical procedure).
  • Cohort study (cause → effect = Prospective):
    • Analyzes risk factors by following a group of disease-free individuals and uses correlations to determine the absolute risk of disease contraction.
    • The comparison group may be the general population or another cohort.
    • Can be retrospective, using archived records.
  • Case-control study (effect → cause = Retrospective):
    • Compares two existing groups with differing outcomes based on a supposed causal attribute.
    • Compares individuals with the condition/disease (“cases”) to similar individuals without the condition (“controls”).
    • Advantages: Relatively inexpensive, can be conducted by small teams, shorter duration.
    • Disadvantage: Difficulty obtaining reliable information about past exposure status.
    • Example: Demonstrating the link between tobacco smoking and lung cancer.

2. Transversal Study (Cross-Sectional Study)

  • Observes a population or a representative subset at a specific point in time.
  • Differs from case-control studies by providing data on the entire population, not just those with a specific characteristic.
  • Data is collected at a defined time.
  • Often used to assess the prevalence of acute or chronic conditions.