Communication: Reply to Fox and Schruben
In the recent issue of Management Science Fox Fox, B. 1978. Estimation and simulation. Management Sci.24 8, April 860--861. expressed doubts about the relevance of steady-state behavior. In a reply Schruben Schruben, L. W. 1978. Reply to Fox. Management Sci.24 8, April 862. disagreed on this point. With Fox he was in favor of publishing failures of variance reduction techniques VRT's. I would like to add the following remarks.
Variance reduction through smoothing and control variates for Markov chain simulations
We consider the simulation of a discrete Markov chain that is so large that numerical solution of the steady-state balance equations cannot be done with available computers, We propose smoothing methods to obtain variance reduction when simulation is used to estimate a function of a subset of the steady-state probabilities. These methods attempt to make each transition provide information about the probabilities of interest. We give an algorithm that converges to the optimal smoothing operator, and some guidelines for picking the parameters of this algorithm. Analytical arguments are used to justify our procedures, and they are buttressed by the results of a numerical example,
Proliferative kidney disease: first reported outbreak in North America
Abstract. Proliferative kidney disease (PKD) was diagnosed in rainbow trout, Salmo gairdneri Richardson, at the Hagerman, Idaho, State Fish Hatchery. Wild fish from Riley Creek, one of the hatchery water supplies, were infected with PKD organisms. Clinical signs, gross pathology and histopathology of affected fish were typical of those reported for PKD in salmonids from European hatcheries. In addition to lesions normally seen, we observed a severe vasculitis and occlusion of renal and hepatic vessels. Ultrastructure of the PKD organism and possible inclusion body production sites are described. The disease outbreak was complicated by the presence of other infectious diseases. This is the first recorded outbreak of PKD in North America.