===== Ecological Trend Analysis =====

**Ecological trend analysis** is a type of **descriptive epidemiological study** that examines changes in disease rates, exposures, or health outcomes over time using **population-level (grouped) data**, rather than individual-level information.

==== Key Features ====
  * **Unit of analysis**: groups or populations (e.g., countries, regions, age cohorts), not individuals.
  * **Objective**: to assess **temporal patterns** and **trends** in disease burden, risk factor exposure, or health outcomes.
  * **Data sources**: often derived from national registries, surveys, census data, international databases (e.g., WHO, GBD).
  * **Commonly used in**:
    * Global burden of disease studies
    * Environmental health (e.g., air pollution, climate)
    * Socioeconomic or policy impact assessments
  * **Methods**:
    * Time series analysis
    * Regression models (e.g., Joinpoint, Poisson, or age–period–cohort models)
    * Age-standardized rate comparisons across time

==== Strengths ====
  * Useful for generating hypotheses
  * Enables cross-national or global comparisons
  * Can identify public health priorities and monitor progress over time

==== Limitations ====
  * Subject to **ecological fallacy** — associations at the group level may not hold at the individual level.
  * May be affected by confounding variables that vary between groups or over time.

==== Related Terms ====
  * [[Ecological study]]
  * [[Time trend analysis]]
  * [[Global burden of disease (GBD)]]