JSM 2004 - Toronto

Abstract #300524

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Activity Number: 294
Type: Topic Contributed
Date/Time: Wednesday, August 11, 2004 : 8:30 AM to 10:20 AM
Sponsor: Section on Statistics and the Environment
Abstract - #300524
Title: Conditional Independence Testing in the Weights-of-Evidence Method
Author(s): Frederik P. Agterberg*+
Companies: Geological Survey of Canada
Address: 601 Booth St., Ottawa, ON, K1A 0E8, Canada
Keywords: weights-of-evidence ; conditional independence ; Bayes's rule
Abstract:

Weights-of-Evidence (WofE) modeling is a statistical technique for correlating a pattern of n points for discrete events with p map patterns. Originally based on a medical expert system, WofE was developed for mineral potential mapping using Geographic Information Systems. With software including the WofE Arcview extension freely available on the internet, there now are many users including geoscientists concerned with environmental applications. Today, nearly half of WofE users are biologists interested, for example, in wild life habitats. The indicator map patterns used in practical applications frequently are reduced to binary form. Bayes's rule is used to estimate positive or negative weight for presence or absence, and zero weight is assigned to missing data. The contrast representing the difference between positive and negative weight often is maximized to create a suitable binary map layer. The weights for p map layers are added assuming their conditional independence with respect to the point pattern. The sum of all posterior probabilities for arbitrarily small unit cells in the study region then should be equal to n.

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