Bohdana Ratitch

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In this paper, we advocate the use of Sparse Distributed Memories (SDMs) for on-line, value-based reinforcement learning (RL). SDMs provide a linear, local function approximation scheme, designed to work when a very large/ high-dimensional input (address) space has to be mapped into a much smaller physical memory. We present an implementation of the SDM(More)
Patrolling tasks can be encountered in a variety of real-world domains, ranging from computer network administration and surveillance to computer wargame simulations. It is a complex multi-agent task, which usually requires agents to coordinate their decision-making in order to achieve optimal performance of the group as a whole. In this paper, we show how(More)
The need to use rigorous, transparent, clearly interpretable, and scientifically justified methodology for preventing and dealing with missing data in clinical trials has been a focus of much attention from regulators, practitioners, and academicians over the past years. New guidelines and recommendations emphasize the importance of minimizing the amount of(More)
Problem characteristics often have a significant influence on the difficulty of solving optimization problems. In this paper, we propose attributes for characterizing Markov Decision Processes (MDPs), and discuss how they affect the performance of reinforcement learning algorithms that use function approximation. The attributes measure mainly the amount of(More)
Multiple imputation (MI) is a methodology for dealing with missing data that has been steadily gaining wide usage in clinical trials. Various methods have been developed and are readily available in SAS PROC MI for multiple imputation of both continuous and categorical variables. MI produces multiple copies of the original dataset, where missing data are(More)
Methods for dealing with missing data in clinical trials have been receiving increasing attention from the regulators, practitioners and academicians in the pharmaceutical industry over the past years. New guidelines and recommendations place a great emphasis not only on the importance of carefully selecting primary analysis methods based on clearly(More)
Over the past years, significant progress has been made in developing statistically rigorous methods to implement clinically interpretable sensitivity analyses for assumptions about the missingness mechanism in clinical trials for continuous and (to a lesser extent) for binary or categorical endpoints. Studies with time-to-event outcomes have received much(More)
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