A liberating way to approach experimental design is to take the attitude that you are telling a story, a kind of environmental "who dunnit". How do we translate the "story" into a program? What are the clues or information our environmental detective will need to be certain (s)he has the real culprit arrested? The story usually requires;
evidence of the crime (a "body");
evidence of where and when the crime was committed;
evidence of the way the crime was committed;
the ability to refute any alibis;
a method to focus on potential suspects;
first hand evidence, preferably corroborated;
no untested assumptions;
A good experimental design is not an accident. In the same way that a good story requires effort and clear thinking, and the ability to anticipate the mind of the reader, a good design marshals evidence that is convincing and satisfying.
The selection of indicators is integral to getting the "conviction", needing to meet criteria of relevance and practicality (especially how much you can believe them to provide the evidence you need for this "case").
Experimental designs Types of Design
There are a large number of classes of experimental design. They differ with respect to the relationship between the experimental treatment(s) and the measured response.
The term "non-experimental" is problematic and would include a range of field studies. All these studies are situations where the researcher is not able to manipulate the factors of concern and are primarilytools for generating hypotheses to be tested by subsequent studies. If these studies are to be useful they need to be carried out recognising fully their limitations but with adequate care such that the results obtained are the best possible. Loss of idealism does not justify negligence! These studies have weakened inference, rather than no inference. The consequence is that lack of inference limits the extent that the studies can be extrapolated to other cases.
The U.S. Environmental Protection Agency (USEPA) and the U.S. Geological Survey (USGS developed the following definition of "environmental indicator" as a " ... measurable feature or features that provide managerially and scientifically useful evidence of environmental and ecosystem quality or reliable evidence of trends in quality." Thus, environmental indicators must be:
measurable with available technology,
scientifically valid for assessing or documenting ecosystem quality, and
useful for providing information for management decision making.
Environmental indicators encompass a broad suite of measures that include tools for assessment of chemical, physical, and biological conditions and processes at several levels. These characteristics of environmental indicators have helped define the scope of the group activities.
Dealing with errors
It is essential that the design of your program take into account the kinds of errors that can occur and how to avoid them.
A summary of sorts
Hurlbert (1984) summarises the potential sources of "confusion" in an experiment and means to eliminate or minimise their effect: