"The Measurement of Chronic and Transitory Poverty: with Application to the United States"

This paper proposes a method of measuring chronic and transitory poverty based on any additively-decomposable index of aggregate poverty. Chronic poverty and transitory poverty in the United States are measured using data from the Panel Study of Income Dynamics (1987 interviewing year). In an attempt to identify the most impoverished subpopulations, poverty indices are decomposed according to race, type of household and educational qualifications of the head of the household.

Exact solution of a model for crowding and information transmission in financial markets

An exact solution is presented to a model that mimics the crowding effect in financial markets which arises when groups of agents share information. We show that the size distribution of groups of agents has a power law tail with an exponential cut-off. As the size of these groups determines the supply and demand balance, this implies heavy tails in the distribution of price variation. The moments of the distribution are calculated, as well as the kurtosis. We find that the kurtosis is large for all model parameter values and that the model is not self-organizing

Efficiency and persistence in models of adaptation

A cut-and-paste model which mimics a trial-and-error process of adaptation is introduced and solved. The model, which can be thought of as a diffusion process with memory, is characterized by two properties, efficiency and persistence. We establish a link between these properties and determine two transitions for each property, a percolation transition and a depinning transition. If the adaptation process is iterated, the antipersistent state becomes an attractor of the dynamics. Extensions to higher dimensions are briefly discussed

Democracy versus dictatorship in self-organized models of financial markets

Models to mimic the transmission of information in financial markets are introduced. As an attempt to generate the demand process, we distinguish between dictatorship associations, where groups of agents rely on one of them to make decision, and democratic associations, where each agent takes part in the group decision. In the dictatorship model, agents segregate into two distinct populations, while the democratic model is driven towards a critical state where groups of agents of all sizes exist. Hence, both models display a level of organization, but only the democratic model is self-organized. We show that the dictatorship model generates less-volatile markets than the democratic model

Transition from coherence to bistability in a model of financial markets

We present a model describing the competition between information transmission and decision making in financial markets. The solution of this simple model is recalled, and possible variations discussed. It is shown numerically that despite its simplicity, it can mimic a size effect comparable to a crash. Two extensions of this model are presented that allow to simulate the demand process. One of these extensions has a coherent stable equilibrium and is self-organized, while the other has a bistable equilibrium, with a spontaneous segregation of the population of agents. A new model is introduced to generate a transition between those two equilibriums. We show that the coherent state is dominant up to an equal mixing of the two extensions. We focuss our attention on the microscopic structure of the investment rate, which is the main parameter of the original model. A constant investment rate seems to be a very good approximation

"Female-Headed Families: Why Are They So Poor?"

Over the last few decades in the United States, the poverty rate for female-headed families (with no husband present) has been about three times the poverty rate for male-headed families (with no wife present) and about six times the poverty rate for married- couple families. This paper addresses the question of why, in general, female-headed families are so much poorer than other families. A decomposition of poverty rates and a set of probit models are used to identify the factors which determine the poverty rates for the three family types. The following control variables are found to be important determinants of poverty for all three family types: education of family members; age, race, disability, and unemployment of the family head; geographical location, size and age composition of the family. Both married-couple families and male-headed families are found to be less poor than female-headed families mainly because additional units of those control variables which reduce (increase) poverty have a larger (smaller) impact in the case of the former two family types than in the case of female-headed families. Of lesser importance is the fact that female-headed families, on average, have less (more) of those control variables which reduce (increase) poverty.

"Poverty and Choice of Marital Status: A Self-Selection Model"

Over the last few decades in the United States, the poverty rate for female-headed families has been about five times the poverty rate for other family types. This paper addresses the question of why, in general, female-headed families are so much poorer than other families. Recognizing that individuals choose their own marital status, a self-selection model is used to identify the factors which determine the poverty rates for married- couple families, families headed by females with no husband present, and families headed by males with no wife present. The following control variables are found to be important determinants of poverty for all three family types: education of family members; age, race, disability, and unemployment of the family head; geographical location, size and composition of the family. Both married-couple families and male-headed families are found to be less poor than female-headed families mainly because the marginal effects of the control variables, and to a lesser extent the mean levels of the control variables, favor the former two types of families over female-headed families.

"Poverty and Household Composition"

This paper has investigated the relationship between poverty and family type, as reflected in the marital status and gender of the head of the family number of factors have been identified as important determinants of poverty for all family types: education and work experience of family members, race, disability, and unemployment of the family head, geographical location, size and composition of the family.

Models for the size distribution of businesses in a price driven market

A microscopic model of aggregation and fragmentation is introduced to investigate the size distribution of businesses. In the model, businesses are constrained to comply with the market price, as expected by the customers, while customers can only buy at the prices offered by the businesses. We show numerically and analytically that the size distribution scales like a power-law. A mean-field version of our model is also introduced and we determine for which value of the parameters the mean-field model agrees with the microscopic model. We discuss to what extent our simple model and its results compare with empirical data on company sizes in the U.S. and debt sizes in Japan. Finally, possible extensions of the mean-field model are discussed, to cope with other empirical data.Comment: 12 pages, 2 figures, submitted for publicatio

Strategy Selection in the Minority Game

We investigate the dynamics of the choice of an active strategy in the minority game. A history distribution is introduced as an analytical tool to study the asymmetry between the two choices offered to the agents. Its properties are studied numerically. It allows us to show that the departure from uniformity in the initial attribution of strategies to the agents is important even in the efficient market. Also, an approximate expression for the variance of the number of agents at one side in the efficient phase is proposed. All the analytical propositions are supported by numerical simulations of the system.Comment: Latex file, 17 page, 4 figure