MANUAL No - Forest and Wood Products Australia

Manual No. 8: Termite Attack 47
probability of
termites in suburbs
but not in garden
Figure 4.7. Venn diagram of probabilities of the occurrence of termites at time zero.
The Venn diagram of probabilities at time zero is shown in Figure 4.7. The total
probabilities will be divided into three subgroups defined as follows:
P1 = Probability of termites in the garden
=Pgarden (4.15)
P2 = Probability of termites in the adjoining suburbs but not in the garden
=Psuburb–PsuburbPgarden/suburb (4.16)
P3 = Probability of no termites either in the garden or the adjoining suburbs
=1–Psuburb–Pgarden+PsuburbPgarden/suburb (4.17)
where Pgarden and Psuburb denote the probabilities that there are termites in the garden and the
suburb respectively at time zero, and Pgarden/suburb denotes the probability that there are
termites in the garden, whenever termites are found in the suburb.
Note that
probability of no
termites in garden
or suburbs
all probabilities
(area = 1.0)
probability of
termites in garden
P1+P2+P3=1.0 (4.18)
Note also that for the necessary condition P3 0, it is necessary that Pgarden/suburb Pgarden
when Psuburb = 1.
The mean time taken to destroy a house, based on expert opinion, is then assumed to be
given by
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