MANUAL No - Forest and Wood Products Australia

Manual No. 8: Termite Attack 50
data for Zone 2 may be considered to be average and the values of the constants A and B used
in equations (4.12) are 0.08 and 0.004 respectively. This leads to a value of mean(tmodel) =
44.1 years.
A second estimate of a typical mean(tmodel) can be obtained from the Termite Tally
where the data is grouped according to agro-ecological zones. For this case, the data for the
combined Zones 2 and 3 may be taken as average. For this case, the values of A and B are
found to be 0.04 and 0.004 respectively. This leads to a value of mean(tmodel) = 50.2 years.
The data from the Termite Tally also indicates that for the probability distribution
function of attack times, suitable calibration choices are for a parameter b = 0.0002.
The model matches the Termite Tally data for average hazard zone conditions when the value
of mean(t)=44 yrs is used. Figure 5.1 shows a plot of a distribution with mean(t)=44 years,
and Figure 5.2 shows the same plot compared with the findings of the Termite Tally.
Taking into account the scatter of the Termite Tally data, the model appears to give as
good a fit as can be expected for average conditions. Reasons for the kink and the dotted
extension of the predicted graph in Fig 5.2 can be seen in Fig. 5.1.
probability that house has
been attacked
1.5
1
0.5
0
true risk
mean(t model) = 44.1 years
apparent risk
0 50 100 150 200
age of house (years)
Figure 5.1. Computed risk for the calibration case;
{true risk = P(house, attack, true, t); apparent risk = P(house, attack, obsv, t)}.
50