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 Because
field studies are uncontrolled, they have a higher degree of variability,
and it is often more difficult to detect important changes. Because
many factors are involved, field studies need to be designed to
minimize confounding factors, and must be carefully evaluated.
Studies should be designed to define one or more of the following:
- Exposure in the system of interest.
- Differences in measures of effect between reference sites and
study areas.
- Lack of differences.
Field surveys are often reported as status and trend studies. In
some cases, investigators use an approach that is intermediate between
a laboratory and field study. They perform laboratory tests with
materials collected from the field. This type of study can improve
the power to detect difference and can provide evidence of causality
between the media and ecological effects.
Relevant
guidelines section(s): 4.1.1
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Field
Study Design