A cohort study involves observing the occurrence of health events over time within a defined population, included at the beginning of the study and followed up over several months or years depending on a data collection protocol that has been adapted to the research objectives, which may be health examinations, interviews, biological sampling or medical record analysis for example.

What is a cohort study ?

These studies help to spot and analyze links between diverse exposure factors (genetic, biological, environmental, behavioral, demographic, social, cultural and so on) and the subsequent occurrence of adverse health events (e.g. diseases, accidents, mood swings or behavioral disorders) while the cohort participants are being followed up.

They therefore pave the way to genuinely etiological research as they establish statistically significant links between exposures and/or risk factors and the appearance of negative health events.

Accordingly, they provide reasons for possible causal links between factors or exposures measured and the health events listed. They also create the opportunity for comprehensive research on the sequence over time of mechanisms and processes that lead to somatic or psychological illnesses. This comprehensive research is particularly useful in the field of behavioral risks (e.g. eating disorders or addictive behavior) for the purposes of health education and prevention.

There are two main types of cohort study

"General" cohort studies which usually recruit participants from the general population. These studies cover an open scope of health problems and follow-up may continue over several decades. The GAZEL cohort study, which has been following up a number of current and retired employees of the French electricity company EDF on the basis of a broad spectrum of health indicators, is a good example.

"Thematic" cohort studies which focus on one disease or a family of diseases. Participants may be recruited from among the general population, but usually they come from the clinical population. These studies monitor the occurrence and development over time of the diseases being studied (particularly chronic diseases) as well as the treatment effects with a view to evaluating treatments.

Facts & figures

Within Inserm, 89 cohorts spontaneously declared by researchers are listed in Inserm’s database on research. A significant proportion of these cohorts are thematic: malignant tumors (17), infectious diseases (15), neuropsychiatric disorders (10), cardiovascular diseases (6), musculoskeletal disorders (6), endocrine and metabolic disorders (6).

More generally, 340 investigations are currently under way within some fifty Inserm structures (laboratories, clinical investigation centers, registers):

  • 75% of these involve patients,
  • more than a third are conducted on cohorts,
  • 25% are collecting blood samples and only 2% involve cell and tissue samples,
  • themes concerned: cancer, cardiovascular diseases, ageing, reproduction, nutrition, etc.

News and prospects

In 2008, the Directorate-General for Research and Innovation (French Ministry of Higher Education and Research) and the Directorate-General for Health (French Ministry of Health) decided to set up a procedure for evaluating and selecting large cohorts in the health field with a view to funding them through the "Very Large Research Infrastructures" program (TGIR in French).

An initial call for funding was launched in 2008. The French Public Health Institute (ISP) was entrusted with running the evaluation and funding procedure, with the support of the French Institute for Public Health Research (IReSP), which is a Scientific Interest Group (GIS) placed under the authority of the ISP and federating all public health research partners. This call for funding brought in 96 applications. After the application evaluation procedure, 20 cohort projects were selected and received funding.

A second call for funding will be launched in 2009. A detailed description of the evaluation procedure for this call for funding can be consulted on the IReSP website.

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