Prediction of Occurrence of Discrete Events - Geomathematics: Theoretical Foundations, Applications and Future Developments - page 145

Fig. 5.3 Location of study area with gold deposits in Meguma Terrane, eastern mainland Nova
Scotia (Source: Bonham-Carter et al. 1990 , Fig. 1)

Approximate variances of the weights can be obtained from:

1
nbd

1
nbd ; ˃

1
n bd þ

1
n b d

2 WðÞ ¼ 2 WðÞ ¼

˃

ðÞ þ

where the denominators of the terms on the right sides represent numbers of unit
cells with map layer and deposit present or absent. Spiegelhalter and Knill-Jones
( 1984 ) had used similar asymptotic expressions for variances of weights in their
GLADYS expert system. The following contingency table can be created:

p bd
p bd p b d

nn d =

p b d ðÞ n b d ð = n

n bd = nnb d =

P ¼

n