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Fitting the Triplets Process

 

Let us now consider fitting the triplets process to the same data Figure 1.1 to which we fit the saturation process. We start with stochastic approximation doing the same as we did with the saturation process. Start at the Poisson model with parameter (5.92, 0, 0), making a short run with tex2html_wrap_inline4471 . Here we are a bit more careful, plotting the tex2html_wrap_inline2411 values over the course of the run. Values of tex2html_wrap_inline4475 are shown in Figure 1.3.

   figure1173
Figure 1.3: Time Course of Stochastic Approximation. The stochastic approximation parameter tex2html_wrap_inline2321 was started at tex2html_wrap_inline2323 . It was lowered to tex2html_wrap_inline2325 at iteration 100 thousand, to tex2html_wrap_inline2327 at 200 thousand, and to tex2html_wrap_inline2329 at 300 thousand.

This run was followed by three more short runs with tex2html_wrap_inline2321 values of tex2html_wrap_inline2325 , tex2html_wrap_inline2327 , and tex2html_wrap_inline2329 . All four runs are shown in the figure. The lowering of tex2html_wrap_inline2321 over the course of the runs seems useful. At tex2html_wrap_inline4471 the tex2html_wrap_inline4475 values are all over the lot, at tex2html_wrap_inline4501 the tex2html_wrap_inline4475 convergence is very slow.

The parameter values after each of the four short runs shown in Figure 1.3 and a longer run were

table1188

We follow this with two MCL steps to obtain an accurate estimate.

table1203

In each pair of rows the upper line gives the estimate and the lower gives the Monte Carlo standard error. Our final estimate (4.527, 0.6072, -0.1673) has three to four significant figures of accuracy in the Monte Carlo. The inverse Fisher information is

displaymath4555

and the square root of the diagonal elements is (0.15, 0.076, 0.035), which is 100 times the Monte Carlo error.



Charles Geyer
Fri Jul 5 15:26:21 CDT 1996