Ecological Clinical Study

An Ecological Clinical Study is an Observational Clinical Study that compares clusters of people that are usually grouped based on their geographical location or temporal associations.

• AKA: Ecologic/Community Observational Clinical Trial.
• Context:
  • It is (typically) a retrospective study in which the disease measure is the prevalence and the risk measure is the prevalence ratio.
  • It can range from being a Geographical-Ecological Clinical Study to being a Temporal-Ecological Clinical Study.
  • Strengths/Advantages:
    • very inexpensive;
    • fast;
    • and easy to assign exposure levels.
  • Weaknesses/Disadvantages:
    • inaccuracy of data;
    • inability to control for confounders;
    • difficulty identifying or quantifying denominator;
    • and no demonstrated temporality.
• Example(s):
  • NCT04714008: Covid-19 and ONline GAmbling (CONGA),
  • NCT04123015: Clinical Activity During Night-shift: an Ecological Study,
  • NCT03271593: Impact of Rotavirus Vaccination on Hospital Pressures at a Large Paediatric Hospital in the UK: an Ecological Study,
  • NCT00843115: Observational Study Of Donepezil In Routine Clinical Practice,
  • …
• Counter-Example(s):
  • Case-Control Clinical Study,
  • Case-Crossover Clinical Study,
  • Cohort Clinical Study,
  • Cross-Sectional Clinical Study,
  • Proportional Mortality Ratio Clinical Study.
• See: Clinical Exposure Measure, Clinical Exposure-Outcome Relationship, Descriptive Clinical Trial, Diagnostic Clinical Trial, Interventional Clinical Trial, Uncontrolled Clinical Intervention Study.

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References

2016

• (Grant, 2016) ⇒ William B. Grant (2016). "The role of geographical ecological studies in identifying diseases linked to UVB exposure and/or vitamin D". In: Dermato Endocrinology 8(1):e1137400. DOI:10.1080/19381980.2015.1137400.
  • QUOTE: Ecological studies can be of 2 types:
    • Geographical. Health outcomes and risk-modifying factors are averaged for populations divided along geographical lines.
    • Temporal. Health outcomes are examined for seasonal variations or trends

(...)

Ecological studies have played important roles in understanding how diet affects risk of disease. A 1975 multicountry ecological study linked dietary factors to cancer incidence rates in 23 countries and mortality rates in 32 countries.

2014a

• (Loney & Nagelkerke, 2014) ⇒ Tom Loney, and Nico J. Nagelkerke (2014). "The individualistic fallacy, ecological studies and instrumental variables: a causal interpretation". In: Emerging Themes in Epidemiology, 11(18).
  • QUOTE: Ecological studies are epidemiological investigations in which either the units of analysis are populations or groups of people, as opposed to individuals, or exposures are only known at the population level while outcomes may be known at the individual level. Specifically, ecological variables are properties of groups, organisations, or places, whereas individual-level variables are properties of each person. Generally, public and environmental health researchers utilise ecological study designs to explore potential causal associations between one or more exposures and a specific health outcome when alternative study designs (e.g. case–control, cohort, randomised controlled trial) are not possible or relevant. For example, an ecologic study is the most appropriate research design if we were interested in the effect of a macro-level governmental policy change, such as an inner-city traffic congestion charge to reduce carbon emissions and improve air quality, on a particular aggregate health outcome (e.g. number of consultations for childhood respiratory disorders).

2014b

• (Thiese, 2014) ⇒ Matthew S. Thiese. (2014). “Observational and Interventional Study Design Types; An Overview.” In: Biochemia Medica (Zagreb). Journal, 24(2).
  • QUOTE: The most basic observational study is an ecological study. This study design compares clusters of people, usually grouped based on their geographical location or temporal associations (...). Ecological studies assign one exposure level for each distinct group and can provide a rough estimation of prevalence of disease within a population. Ecological studies are generally retrospective. An example of an ecological study is the comparison of the prevalence of obesity in the United States and France. The geographic area is considered the exposure and the outcome is obesity. There are inherent potential weaknesses with this approach, including loss of data resolution and potential misclassification (...). This type of study design also has additional weaknesses. Typically these studies derive their data from large databases that are created for purposes other than research, which may introduce error or misclassification (...). Quantification of both the number of cases and the total population can be difficult, leading to error or bias. Lastly, due to the limited amount of data available, it is difficult to control for other factors that may mask or falsely suggest a relationship between the exposure and the outcome. However, ecological studies are generally very cost effective and are a starting point for hypothesis generation.

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