摘要：

In many large-scale conservation or ecological problems where experiments are intractable or unethical, regression methods are used to attempt to gauge the impact of a set of nominally independent variables (X) upon a dependent variable (Y). Workers often want to assert that a given X has a major influence on Y, and so, by using this indirection to infer a probable causal relationship. There are two difficulties apart from the demonstrability issue itself: (1) multiple regression is plagued by collinear relationships in X; and (2) any regression is designed to produce a function that in some way minimizes the overall difference between the observed and <img src="/content/W18T336XGM8Q7773/xxlarge8216.gif" alt="lsquo" align="BASELINE" border="0">predicted<img src="/content/W18T336XGM8Q7773/xxlarge8217.gif" alt="rsquo" align="BASELINE" border="0"> Ys, which does not necessarily equate to determining probable influence in a multivariate setting. Problem (1) may be explored by comparing two

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