3_bacips

3_bacips - Introduction Estimating Effect Size of an...

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Introduction Page 1 Estimating Effect Size of an Ecological Impact from a “Before-After-Control-Impact-Paired-Series” Design (adapted from Bence et al., Osenberg and Schmitt, In Detecting Ecological Impacts: Conceptual Issues and Applications in Marine Habitats , 1995, R.J. Schmitt and C.W. Osenberg (Editors) Background: Ecologists and environmental scientists have long sought to provide accurate scientific assessments of the environmental ramifications of human activities. Replicated manipulative field experiments, while best suited to ascribe a causal role to the effects human activities on the environment, are rarely feasible when large scale disturbances are considered. For example, it would not be practical or desirable to construct a series of functioning nuclear power plants along the coast of California merely to examine the impacts of such facilities on the marine environment. Hence, Field Impact Assessments must rely on different methods. Four potential experimental designs include: Control-Impact, Before- After, BACI, and BACIPS. Introduction to 4 Impact Assessment Designs: The Control-Impact Design: Perhaps the most common Field Assessment design involves the comparison of a series of control sites (places far enough from the activity to be relatively unaffected by it) and a series of impact sites (i.e., near the activity and thus expected to show signs of an effect if one exists). Such a design is useful if no Before data is available (i.e., an oil spill occurs at a remote location off the coast of Alaska--no baseline data on this region exists). Results may be confounded by natural spatial variation. The Before-After Design: An alternate design requires sampling of an Impact site both Before and After the activity or disturbance. Sampling is replicated through time. A comparison of data collected Before and After suggest the presence or absence of a disturbance. This design is useful if no appropriate “Control” sites exist (i.e., Impact site is unique), however it is always desirable to have a control when possible. In this design, results may be confounded by natural temporal variation. The Before-After-Control-Impact (BACI) Design:
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This note was uploaded on 08/06/2008 for the course ESM 260 taught by Professor Lenihan during the Spring '08 term at UCSB.

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3_bacips - Introduction Estimating Effect Size of an...

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