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The Canary Database
Yale Occupational and Environmental Medicine Program
135 College St
Room 366
New Haven, CT, USA

Study methodologies: Experimental

The Canary database curators determine, for each included study, the type of study methodology employed by the researchers (using this classification protocol). The possible categories are:

Fox has outlined criteria for objectively evaluating the relationship between an environmental hazard and an observed health effect in an observational study of animals (Fox 1991). These include probability, time order, strength of association, specificity, and consistency on replication, predictive performance, and coherence. The choice of study design can have a major effect on the ability of a study to fulfill such criteria.

Our preliminary review of the animal sentinel literature has found that some potentially useful study designs, such as case-control and cohort, are under-utilized in animal sentinel research.

Experimental Studies

Researchers often study environmental toxins in the controlled setting of the laboratory. The Canary Database looks for such studies that use "non-traditional" animal species representative of free-ranging or domestic populations. Sometimes it is difficult to determine whether a laboratory experiment was using animals derived from a truly wild (or free ranging domestic) population rather than one bred strictly for laboratory use. Some experimental studies in the database ventured outside the laboratory to test the effect of slightly less controlled exposures. One team maintained fish in a tank connected with a polluted river compared to controls raised in tap water (Schmidt-Posthaus, Bernet et al. 2001). Such "enclosure" studies blur the distinction between a tightly controlled laboratory experiment, and the uncontrolled exposure situation in an observational cohort study. Infectious disease studies also use experimental designs, though much less commonly, and usually in conjunction with another study methodology.

Due to the fact that many variables can be tightly controlled, experimental studies can provide invaluable confirmation of an association between an exposure and an outcome. Yet in the overall investigation of an environmental hazard or an unexplained health outcome in a population, the experimental design has limitations. Constructing a controlled environment in the laboratory setting and maintaining a laboratory population of animals can be expensive and time consuming. The laboratory setting may also fail to replicate some of the important forces at work in the environment. For logistic reasons, experimental doses may be higher and follow-up time shorter. Artificial diets and limitations on activity may also make it difficult to extrapolate experimental findings to the real world setting. Perhaps most importantly, an experiment can only test a very limited set of hypotheses. Therefore, experiments would seem most appropriate only after a number of observational studies have consistently provided support for a limited number of hypotheses.

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