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Table 5.10
Meguma Terrane example. Weights and adjusted weights
New
contrast
W
+
W
New W
+
New W
Variable
Contrast B
Anticlines
0.54559
0.81603 1.36162
0.91524
0.49935
0.74686
1.24621
Au in balsam fir
0.65006
0.25920 0.90927
1.16490
0.75726
0.30194
1.05920
GH contact
0.35704
0.26256 0.61961
0.45987
0.16419
0.12074
0.28494
Goldenville
0.30231
1.45564 1.75795
0.73623
0.22257
1.07168
1.29425
Devonian granite 0.21771
0.03706 0.25476
1.80401
0.39274
0.06686
0.45960
Geochemistry
0.85240
0.08388 0.93628
0.75700
0.64527
0.06350
0.70877
NW lineaments
0.03998
0.01011 0.05009
0.65798
0.02631
0.00665
0.03296
Source: Agterberg (
2011
, Table 6)
The new approach advocated in this section results in unbiased estimates of the
posterior probabilities. An additional advantage of this approach is that it automat-
ically copes with missing data on some layers because weights of unit areas with
missing data can be set equal to zero as is generally practiced in WofE applications.
As usual, the method presented here was applied using known events in the study
area only.
Because logistic regression results in posterior probabilities that are unbiased in
the sense that the condition
S
total number of
events) is satisfied, it is possible to modify the WofE further by assigning other
values to the pixels or unique conditions that contain events as discussed and
applied by Zhang et al. (
2013
).
¼
N
(sum of posterior probabilities
¼
References
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Agterberg FP (1984) Use of spatial analysis in mineral resource evaluation. Math Geol
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Agterberg FP (1989a) Computer programs for mineral exploration. Science 245:76-81
Agterberg FP (1989b) Systematic approach to dealing with uncertainty of geoscience information
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the mineral industry, Las Vegas, March 1989. Society of Mining Engineers, AIME, Littleton,
pp 165-178
Agterberg FP (1989c) LOGDIA, Fortran 77 program for logistic regression with diagnostics.
Comput Geosci 15:599-614
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Agterberg FP, Bonham-Carter GF (1990) Deriving weights of evidence from geoscience contour
maps for the prediction of discrete events. In: Proceedings of the 22nd APCOM symposium,
Technical University of Berlin, vol 2, pp 381-396
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