On the convergence of reinforcement learning

This paper examines the convergence of payoffs and strategies in Erev and Roth's model of reinforcement learning. When all players use this rule it eliminates iteratively dominated strategies and in two-person constant-sum games average payoffs converge to the value of the game. Strategies converge in constant-sum games with unique equilibria if they are pure or if they are mixed and the game is 2×2. The long-run behaviour of the learning rule is governed by equations related to Maynard Smith's version of the replicator dynamic. Properties of the learning rule against general opponents are also studied.     

Queues and Hierarchies

This paper examines the optimal structure of hierarchies when workers differ in the range of tasks they can perform. A hierarchical system may reduce costs by allowing most tasks to be handled by unskilled workers. This may however increase delay for those tasks which must pass through several layers before reaching the appropriate level. The paper characterises an optimal hierarchy when such a trade-off exists.     

Participatory appraisal approaches versus sample survey data collection: a case of smallholder farmers well-being ranking in Njombe District, Tanzania

Social scientists and rural development interventionists inTanzania and in Sub-Saharan Africa depend mainly on conventionalsample surveys; in part this is a legacy of their basic training.Participatory rural appraisal and intervention approaches offera varied range of methods. We ask ourselves whether the resultsfrom participatory, rapid appraisals are conflicting and differentto those from sample surveys? This paper compares results ofa Rapid Participatory Rural Appraisal (PRA) with a conventionalsample survey. These surveys were conducted at the end of 1995and mid-1996 respectively, to establish socio-economic well-beingranks in Njombe district. A comparison of results shows thatthe well-being ranks established using PRA are valid and theapproach is reliable. The three qualitatively established well-beingranks differed empirically in many socio-economic indicators.These include resource endowment, labour force size, agriculturalland, livestock ownership, forest woodlot management, perceptionof food insecurity, technological advances in agricultural productionand natural resource management systems. Results show that thelow well-being group and female-headed households are disadvantaged.The goal of the Hifadhi Ya Mazingira-Njombe project is to developenvironmentally sustainable crop and livestock husbandry practicesin the district. The well-being ranking exercise has strongimplications for the project's strategy. We discuss the adoptedmethodology and implications. The paper recommends that developmentprogrammes and workers in Tanzania and Sub-Saharan Africa oughtto extend their approaches. It is time to include more of theparticipatory, relatively rapid rural appraisal and interventiontechniques. Benefits that they may accrue are time saving, lowercosts, quality information and stakeholder involvement.     

Education and the natural rate of unemployment

We show how changes in the educational composition of the labourforce affect both the level and the behaviour over time of aggregateunemployment series. We also demonstrate that if it had notbeen for such changes, the US unemployment series would look'European' since the within-group unemployment series all havethat same appearance. We derive a natural-rate model of unemploymentfor two education groups, providing microfoundations for inter-groupdifferences in wages and unemployment, and evaluate its plausibilityin light of microeconomic evidence.     

Welfare policy and the transformation of social security in South Africa

Social security is based on the belief that all citizens should be protected by the state against the main vicissitudes of life: old age, unemployment, disability and sickness. The success of welfare programmes internationally in improving poverty, income distribution and unemployment is appraised. Income maintenance in South Africa, which is discriminatory and ineffective in meeting real human needs, is examined. Although welfare should not promote dependence, neither should it be so hard to come by as to punish the poor.     

On the efficiency of stock-based compensation

When the market can observe the profitability of all projectswith equal precision, then with stock compensation (i) the weighton any given project in managerial compensation is independentof the marginal productivity of effort in the project; (ii)the projects that are the noisiest indicators of managerialeffort receive the most weight in compensation; and (iii) investorshave the greatest incentive to collect information about projectsthat are the noisiest indicators of managerial effort.     

Suicide as an indicator of quality of life: evidence from dialysis patients

Quality of life has been measured in many different ways for patients with chronic medical conditions. What is unique about the approach used here is that it uses suicide rates as a relatively objective measure of quality of life within the population of dialysis patients. Using a Heckman selection model, we estimate the relative suicide rates across patients undergoing both hemodialysis and peritoneal dialysis. Our empirical results show that patients on hemodialysis have relatively lower suicide rates after controlling for other factors. Specifically, our results indicate that 141 fewer suicides will occur for every 1,000 patients shifted from peritoneal to hemodialysis. Prior estimates of the higher costs of the latter modality yield an estimated expenditure of $42,043 per suicide avoided.     

Waiting times and equilibrium selection

Summary. This paper shows how graphs can be used to calculate waiting times in models of equilibrium selection. It also shows how reducing the state space can simplify the calculations of both waiting times and selected equilibria. The results are applied to potential games and games with strategic complementarities.Received: 31 December 2002, Revised: 25 October 2003, JEL Classification Numbers: C72, C73.Alan Beggs: I am grateful to an anonymous referee for helpful comments.     

Cost effectiveness analysis of a next generation risk assessment score for cardiovascular disease

Objectives:

The goal of this study is to determine the cost-effectiveness of MIRISK VP, a next generation coronary heart disease risk assessment score, in correctly reclassifying and appropriately treating asymptomatic, intermediate risk patients.

Study design:

A Markov model was employed with simulated subjects based on the Multi-Ethnic Study of Atherosclerosis (MESA). This study evaluated three treatment strategies: (i) practice at MESA enrollment, (ii) current guidelines, and (iii) MIRISK VP in MESA.

Methods:

The model assessed patient healthcare costs and outcomes, expressed in terms of life years and quality-adjusted life years (QALYs), over the lifetime of the cohort from the provider and payer perspective. A total of 50,000 hypothetical individuals were used in the model. A sensitivity analysis was conducted (based on the various input parameters) for the entire cohort and also for individuals aged 65 and older.

Results:

Guiding treatment with MIRISK VP leads to the highest net monetary benefits when compared to the ‘Practice at MESA Enrollment’ or to the ‘Current Guidelines’ strategies. MIRISK VP resulted in a lower mortality rate from any CHD event and a modest increase in QALY of 0.12–0.17 years compared to the other two approaches.

Limitations:

This study has limitations of not comparing performance against strategies other than the FRS, the results are simulated as with all models, the model does not incorporate indirect healthcare costs, and the impact of patient or physician behaviors on outcomes were not taken into account.

Conclusions:

MIRISK VP has the potential to improve patient outcomes compared to the alternative strategies. It is marginally more costly than both the ‘Practice at MESA Enrollment’ and the ‘Current Guidelines’ strategies, but it provides increased effectiveness, which leads to positive net monetary benefits over either strategy.