ABSTRACT
The concept of signi™cance in the context of NEPA is not identical to the concept of signi™cance in statistics. Statistical signi™cance is a mathematical concept using calculations to compare quantitative differences between numerical data sets re¥ecting multiple conditions or experimental treatments. Scientists rely on statistical calculation procedures to test hypotheses regarding the presence of meaningful differences between measured outcomes of experiments or suspected trends in quantitative observations. Statistics ™nds applications in most natural and social sciences. With NEPA the term “signi™cance” is determined more judgmentally, requiring the careful weighing of both quantitative and qualitative evidence by multidisciplinary teams of experts. Statistical signi™cance is expressed using numerical values whereas NEPA signi™cance is usually expressed as either “signi™cant” or “not signi™cant” (or “insigni™cant”), although some NEPA documents do acknowledge broad classes of signi™cance. Statistical signi™cance can be used in any context where there are differing sets of quantitative data, whereas NEPA signi™cance is limited to assessing impacts of actions on baseline conditions.
