Be careful with ecological associations

Nephrology, vol. 26, pp. 501–505

Abstract

Ecological studies are observational studies commonly used in public health research. The main characteristic of this study design is that the statistical analysis is based on pooled (i.e., aggregated) rather than on individual data. Thus, patient-level information such as age, gender, income and disease condition are not considered as individual characteristics but as mean values or frequencies, calculated at country or community level. Ecological studies can be used to compare the aggregated prevalence and incidence data of a given condition across different geographical areas, to assess time-related trends of the frequency of a pre-defined disease/condition, to identify factors explaining changes in health indicators over time in specific populations, to discriminate genetic from environmental causes of geographical variation in disease, or to investigate the relationship between a population-level exposure and a specific disease or condition. The major pitfall in ecological studies is the ecological fallacy, a bias which occurs when conclusions about individuals are erroneously deduced from results about the group to which those individuals belong. In this paper, by using a series of examples, we provide a general explanation of the ecological studies and provide some useful elements to recognize or suspect ecological fallacy in this type of studies.

Authors 8

1. Stefanos K. Roumeliotis

   Aristotle University of Thessaloniki · AHEPA University Hospital

   Affiliation as printed

   Division of Nephrology and Hypertension, 1st Department of Internal Medicine, AHEPA Hospital, School of Medicine Aristotle University of Thessaloniki Thessaloniki Greece

   Division of Nephrology and Hypertension, 1st Department of Internal Medicine, AHEPA Hospital, School of Medicine, Aristotle University of Thessaloniki, Thessaloniki, Greece

2. Samar Abd ElHafeez

   Alexandria University

   Affiliation as printed

   Epidemiology Department High Institute of Public Health‐Alexandria University Alexandria Egypt

   Epidemiology Department, High Institute of Public Health-Alexandria University, Alexandria, Egypt

3. Kitty J. Jager

   Amsterdam UMC Location University of Amsterdam · Amsterdam Public Health · University of Amsterdam

   Affiliation as printed

   Department of Medical Informatics, Academic Medical Center, Amsterdam Public Health Research Institute| University of Amsterdam Amsterdam The Netherlands

   Department of Medical Informatics, Academic Medical Center, Amsterdam Public Health Research Institute|, University of Amsterdam, Amsterdam, The Netherlands

4. Friedo Wilhelm Dekker Aachen Department of Clinical Epidemiology Leiden University Medical Center Leiden The Netherlands Department of Clinical Epidemiology

   Leiden University Medical Center

   Affiliation as printed

   Department of Clinical Epidemiology Leiden University Medical Center Leiden The Netherlands

   Department of Clinical Epidemiology, Leiden University Medical Center, Leiden, The Netherlands

5. Vianda S Stel

   Amsterdam UMC Location University of Amsterdam · Amsterdam Public Health · University of Amsterdam

   Affiliation as printed

   Department of Medical Informatics, Academic Medical Center, Amsterdam Public Health Research Institute| University of Amsterdam Amsterdam The Netherlands

   Department of Medical Informatics, Academic Medical Center, Amsterdam Public Health Research Institute|, University of Amsterdam, Amsterdam, The Netherlands

6. Annalisa Pitino

   Istituto di Fisiologia Clinica · National Research Council

   Affiliation as printed

   Institute of Clinical Physiology (IFC‐CNR) Rome Italy

   Institute of Clinical Physiology (IFC-CNR), Rome, Italy

7. Carmine Zoccali

   Istituto di Fisiologia Clinica · National Research Council

   Affiliation as printed

   Institute of Clinical Physiology (IFC‐CNR) Clinical Epidemiology and Physiopathology of Renal Diseases and Hypertension of Reggio Calabria Reggio Calabria Italy

   Institute of Clinical Physiology (IFC-CNR), Clinical Epidemiology and Physiopathology of Renal Diseases and Hypertension of Reggio Calabria, Reggio Calabria, Italy

8. Giovanni Luigi Tripepi corresponding

   Istituto di Fisiologia Clinica · National Research Council

   Affiliation as printed

   Institute of Clinical Physiology (IFC‐CNR) Clinical Epidemiology and Physiopathology of Renal Diseases and Hypertension of Reggio Calabria Reggio Calabria Italy

   Institute of Clinical Physiology (IFC-CNR), Clinical Epidemiology and Physiopathology of Renal Diseases and Hypertension of Reggio Calabria, Reggio Calabria, Italy