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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