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The Canary Database
Yale Occupational and Environmental Medicine Program
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Study methodologies: Descriptive

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.

Descriptive Studies (Case Reports)

Studies are classified as descriptive case reports if there were no analytic comparisons between groups reported. This is a common type of study methodology for animal sentinel studies. For example, a toxin study reported on the effect of crude oil on seabirds, but did not compare exposed and unexposed animals (Khan and Ryan 1991). Similarly, a study of Leishmaniasis described cutaneous lesions in two individual rodents without further analysis (Morsy, Bassili et al. 1987).

Descriptive case reports can be quick, relatively easy to perform, and therefore useful for generating hypotheses. They are therefore often the first type of study to undertake in the investigation of a suspected hazard or outbreak of disease in an animal population, where it is necessary to describe the outbreak in terms of time, place, and animals affected. Such descriptive reports, however, are unable to analyze cause and effect relationships and provide measures of the strength of association of such relationships.


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