Biomedical subjects

D P Foster

Publications and source records attributed to D P Foster.

3 recordsLinked to original sources

PubMed2003

Corner-transfer-matrix renormalization-group method for two-dimensional self-avoiding walks and other O(n) models.

We present an extension of the corner-transfer-matrix renormalization-group (CTMRG) method to O(n) invariant models, with particular interest in the self-avoiding walk class of models [O(n=0)]. The method is illustrated using an interacting self-avoiding walk model. Based on the efficiency and versatility, when compared to other available numerical methods, we present the CTMRG as the method of choice for two-dimensional self-avoiding walk problems.

Journal Article↗

PubMed2001

On the impossibility of predicting the behavior of rational agents.

A foundational assumption in economics is that people are rational: they choose optimal plans of action given their predictions about future states of the world. In games of strategy this means that each player's strategy should be optimal given his or her prediction of the opponents' strategies. We demonstrate that there is an inherent tension between rationality and prediction when players are uncertain about their opponents' payoff functions. Specifically, there are games in which it is impossible for perfectly rational players to learn to predict the future behavior of their opponents (even approximately) no matter what learning rule they use. The reason is that in trying to predict the next-period behavior of an opponent, a rational player must take an action this period that the opponent can observe. This observation may cause the opponent to alter his next-period behavior, thus invalidating the first player's prediction. The resulting feedback loop has the property that, a positive fraction of the time, the predicted probability of some action next period differs substantially from the actual probability with which the action is going to occur. We conclude that there are strategic situations in which it is impossible in principle for perfectly rational agents to learn to predict the future behavior of other perfectly rational agents based solely on their observed actions.

Forecasting↗

PubMed1981

Met and unmet demand for hospital beds. Some recent evidence.

Many commentators have noted the interrelation of demand and supply of hospital beds and have suggested that an increase in the supply of hospital beds tends to generate additional demand either in the form of more patients admitted or patients treated for longer periods of time or some combination of the two. We can report that the bed use rate can be predicted more accurately in terms of the five-seventh rule, that is if a National Health Service bed is made available for an additional week, then for five out of seven days it will be occupied. This rule was found to apply at both regional and district level. Variation in admission rates was also investigated and it was found that a large proportion of the observed variation could be explained in terms of one variable--bed supply. In view of the Resource Allocation Working Party's proposals, the relationship between the overall standardized mortality ratio and bed supply, admissions rate and bed use rate was investigated. No significant effect, however, was discovered. In other words, it is bed supply which strongly influences the demand for hospital care and not the overall standardized mortality ratio.

Bed Occupancy↗