Nancy Brandon Tuma

Spatial and Temporal Heterogeneity in Diffusion

Standard models of diffusion assume spatial and temporal homogeneity. This article develops a class of diffusion models that incorporate spatial and temporal heterogeneity by turning to the individual level within an event-history framework. These models permit the analyst to represent social structural relations thought to channel diffusion, and to model decay in the influence of events over time. Heterogeneous diffusion models are applied to a reanalysis of data reported in Coleman, Katz, and Menzels classic diffusion study. Network centrality and local structures of influence based on cohesive relations and structural equivalence are all shown to channel the diffusion of tetracycline.

Dynamic Analysis of Event Histories

There is wide interest among sociologists in the study of change but little reflection of this interest in sociological research methods. In this paper we consider the advantages of and procedures of dynamic analysis of event-history data-data givin the number, timing, and sequence of changes in a categorical dependent variable. We argue for grounding this analysis in a continuous-time stochastic model. This permits the data to be fully utilized; it also allows a unified treatment of the various outcomes analyzed in the many approaches that use only part of the information contained in such data. We focus on the familiar continuos-time Markov model, summarize its properties, report its implications for various outcomes, describe extensions to deal with population heterogeneity and time dependence, and outline a maximum-likelihood procedure for estimating the extended model from event-history data. The discussion in illustrated with an empirical analysis of the effects of an income-maintenance experiment on change in marital status. We conclude by contrasting event-history analysis with cross-sectional analysis, event-count analysis, and panel analysis. We find that event-history analysis has substantial advantages over the other approaches.

ENTRY INTO MARRIAGE AND PARENTHOOD BY YOUNG MEN AND WOMEN: THE INFLUENCE OF FAMILY BACKGROUND

We investigate the influence of family background on early entry into marriage and parenthood among white, Hispanic, and black men and women ages 14 to 22 in the first (1979) wave of the National Longitudinal Survey of Youth. Family background is highly associated with early entry into marriage for whites of both genders and female Hispanics and also with early entry into parenthood for all groups except black males. Large group differences in family characteristics explain most of the difference between white and Hispanic women in early marriage and parenthood and about half the difference in early parenthood between black and white women but do not explain the observed variations among other race-gender groups.

Income and Marital Events: Evidence from an Income-Maintenance Experiment

In this paper we report estimates of the impacts of the Seattle and Denver Income-Maintenance Experiments on marital dissolution and remarriage. To assess the experimental impacts, we use a stochastic model of rare events in which the rate at which an event occurs is assumed to depend log linearly on a set exogenous variables. Overall, income maintenance raises the rate of marital dissolution. For black, white, and Chicana women, the greatest increase occurs at the support levels closest to the control situation. The impact of income maintenance on remarriage differs by race-ethnicity. For Chicanas, the rate of remarriage decreases as the level of support increase. For blacks and whites, income maintenance has no discernible impact on the rate of remarriage. The results provide empirical evidence that a change in economic situation does affect marital events in low-income populations.

Income and Independence Effects on Marital Dissolution: Results from the Seattle and Denver Income-Maintenance Experiments

Using data from the Seattle and Denver Income-Maintenance Experiments, this paper discusses the effects of income and changes in income on marital dissolution. In an earlier article, we presented evidence of an experimental impact on marital dissolution and discussed how the pattern of effects found could be accounted for by nonlinear income and independence effects. The income effect decrease the marital dissolution rate by increasing the familys economic well being. The independence effect increase the dissolution rate by reducing the economic dependence of the more dependent partner (usually the wife) on the marriage. In this article, we present a model of nonlinear income and independence effects that accounts for much of the experimental-control difference reported in the earlier paper. According to the model, the effect of an income-maintenance program on marital dissolution depends not only upon the magnitude of the payment a couple receives but also on their level of income before the program, the level of the wifes independence, and the magnitude of the change in the wifes independence.

Classroom Effects on Changes in Children's Friendships.

Previous studies of the effects of classroom characteristics on educational outcomes have been concerned primarily with cognitive outcomes, such as academic achievement. In this paper we examine effects of classroom variables on childrens social development. We argue that the way teachers group students for instructional purposes and their pedagogical techniques affect childrens proximity and similarity within the classroom, and that these in turn affect their interpersonal relationships. We use longitudinal data from fourth, fifth, and sixth grade children to test several hypotheses predicting influences of instructional organization on the formation and stability of childrens friendships. The findings provide evidence that selected classroom variables have a positive impact on the stability of childrens existing friendships and on the likelihood that children become more friendly. The results also indicate that weak friendships are more easily influenced by classroom characteristics than close friendships.

Nonparametric and Partially Parametric Approaches to Event-History Analysis

I have benefited greatly from discussions with Gary Chamberlain and other participants in the Longitudinal Data Analysis Workshop, sponsored by the National Opinion Research Center, 31 July-12 August 1979. James S. Coleman, Michael T. Hannan, Camille Marder, Burton Singer, Louise Smith-Donals, Larry Wu, and an anonymous referee made helpful comments on an earlier draft. The research on Monte Carlo experiments was done in collaboration with Glenn R. Carroll, Michael T. Hannan, and Barbara Warsavage; it was supported by the National Institute of Education under grant number NIE-G-76-0082. Preparation of the other portions of this chapter was supported by the National Science Foundation under grant number NSFSOC-78-123 15. This chapter contains excerpts from Social Dynamics: Models and Methods, coauthored by Michael T. Hannan.

SPECIFICATION AND ESTIMATION OF HETEROGENEOUS DIFFUSION MODELS

Heterogeneous diffusion models let one combine the analysis of intrinsic propensities with that of intrapopulation contagion, and to disaggregate contagion effects into individual susceptibilities, the infectiousness of prior adopters, and the social proximity of prior-potential adopter pairs. This paper reports the results of a series of Monte Carlo simulation studies that investigate estimation issues for this class of models. Graphical analysis of population-level hazard rates is shown to provide little insight into these processes. We focus on the properties of maximum likelihood estimators, considering variation across parameter values and differentforms of model misspecification. When models are correctly specified, we find few conditions under which estimation appears problematic. Difficult cases involve binary networks where network linkages have very strong effects or network density is high. Estimation deteriorates in

Youth Employment: Does Life Begin at 16?

Theoretical economic models, official labor force statistics, and most empirical studies of young workers disregard employment experience of students under age 16. Evidence from several sources, however, suggests that students ages 14 and 15 acquire substantial employment experience. Moreover, that experience is vastly different for black and white youths. Several policy-related issues, including causes of black-white differences in adult earnings, may deserve to be interpreted differently in the light of differentials in early employment experience. This employment experience of 14- and 15-year-olds in general and its racial pattern in particular should not continue to be ignored.

The Effects of Negative Income Tax Programs on Marital Dissolution

We review the reasons for expecting a negative income tax (NIT) to affect marital dissolution rates and present a stochastic model of marital dissolution. The analysis reveals that the experimental NIT programs increased the martial dissolution rates for blacks and whites but not Chicanos. The differences in the magnitude of the responses by NIT guarantee level suggest that there are nonpecuniary differences between the experimental programs and existing income-support programs. We compare the Seattle and Denver Income Maintenance Experiments findings with the findings from the other income maintenance experiments and discuss implications for welfare reform.