Demographers and Their Journals: Who Remains Uncited After Ten Years?

This research note examines the level of uncitedness and the impact of articles published in the years 1990–92 in 17 demography journals. After ten years 24 percent of the demography articles are still uncited and the average number of citations per article is seven. The ten‐year citation history reveals two novel insights. First, the impact of demography journals does not slow down significantly over time. The average number of citations in the first five years hardly differs from the average in the second five years, which suggests that one should be patient in assessing the full effect of demography articles. Second, the chance of being cited for the first time does not depend on the length of time an article remains uncited. In other words, the stigma of uncitedness does not play a significant role in the allocation of citations.     

Testing the relationship between income inequality and life expectancy: a simple correction for the aggregation effect when using aggregated data

In this paper, we show a simple correction for the aggregation effect when testing the relationship between income inequality and life expectancy using aggregated data. While there is evidence for a negative correlation between income inequality and a population’s average life expectancy, it is not clear whether this is due to an aggregation effect based on a non-linear relationship between income and life expectancy or to income inequality being a health hazard in itself. The proposed correction method is general and independent of measures of income inequality, functional form assumptions of the health production function, and assumptions on the income distribution. We apply it to data from the Human Development Report and find that the relationship between income inequality and life expectancy can be explained entirely by the aggregation effect. Hence, there is no evidence that income inequality itself is a health hazard.     

Risk of Extreme Events in Multiobjective Decision Trees Part 2. Rare Events

Earlier work with decision trees identified nonseparability as an obstacle to minimizing the conditional expected value, a measure of the risk of extreme events, by the well-known method of averaging out and folding back. This second of two companion papers addresses the conditional expected value that is defined as the expected outcome assuming that a random variable is observed only in the upper 100 (1 −α) percent of potential outcomes, where α is a cumulative probability preselected by the decision maker. An approach is proposed to overcome the need to evaluate all policies in order to identify the optimal policy. The approach is based in part on approximating the conditional expected value by using statistics of extremes. An existing convenient approximation of the conditional expected value is shown to be separable into two constituent elements of risk and can thus be optimized, along with other objectives including the unconditional expected value of the outcome, in a multiobjective decision tree. An example of sequential decision making for remediation or environmental contamination is provided. The importance of the results for risk analyis beyond the minimization of conditional expected values is pointed out.     

How Influential Are Demography Journals?

This article examines, by means of citation analysis for the years 1991–95, the process of knowledge dissemination in demography journals and the intellectual exchange of demography journals with neighboring social sciences. In addition, it investigates the degree of uncitedness in demography journals. It turns out that a considerable percentage of articles are left uncited: 36 percent of the articles published in demography journals between 1990 and 1992 remained uncited in the five years following their publication. However, these overall uncitedness rates conceal large variations between journals. General-oriented demography journals from the US are well cited. Within the set of demography journals, knowledge flows from general to specialized journals and to a lesser extent the other way round. Specialized journals play a minor role in the construction and exchange of fundamental demographic knowledge. They do, however, influence specific audiences in neighboring social sciences.     

Multivariate τ-estimators for location and scatter

We discuss the robustness and asymptotic behaviour of τ-estimators for multivariate location and scatter. We show that τ-estimators correspond to multivariate M-estimators defined by a weighted average of redescending ψ-functions, where the weights are adaptive. We prove consistency and asymptotic normality under weak assumptions on the underlying distribution, show that τ-estimators have a high breakdown point, and obtain the influence function at general distributions. In the special case of a location-scatter family, τ-estimators are asymptotically equivalent to multivariate S-estimators defined by means of a weighted ψ-function. This enables us to combine a high breakdown point and bounded influence with good asymptotic efficiency for the location and covariance estimator.     

Of rotten kids and Rawlsian parents: The optimal timing of intergenerational transfers

This paper shows that altruistic parents with utilitarian preferences may fare better if they transfer resources to their children early in life instead of delaying the bulk of transfers until after their death. Moreover, the outcome of the analysed “family transfer game” is not Pareto-efficient in the case of bequests. However, if altruistic parents hold Rawlsian preferences, they will be indifferent between gifts and bequests, and Pareto-efficiency is always obtained. In intermediate cases of Atkinson-type welfare functions, welfare losses of bequests compared to gifts disappear as the aversion to inequality converges to infinity. Received: 3 November 1998/Accepted: 4 May 1999     

The effect of conditional heteroskedasticity on common statistical procedures for means and variances

Summary: Commonly used standard statistical procedures for means and variances (such as the t–test for means or the F–test for variances and related confidence procedures) require observations from independent and identically normally distributed variables. These procedures are often routinely applied to financial data, such as asset or currency returns, which do not share these properties. Instead, they are nonnormal and show conditional heteroskedasticity, hence they are dependent. We investigate the effect of conditional heteroskedasticity (as modelled by GARCH(1,1)) on the level of these tests and the coverage probability of the related confidence procedures. It can be seen that conditional heteroskedasticity has no effect on procedures for means (at least in large samples). There is, however, a strong effect of conditional heteroskedasticity on procedures for variances. These procedures should therefore not be used if conditional heteroskedasticity is prevalent in the data.*We are grateful to the referees for their useful and constructive comments.     

Out of Africa: what drives the pressure to emigrate?

Who intends to leave Africa and what drives people to emigrate? For the cases of Ghana, Senegal, Morocco and Egypt, we examined peoples' stated intentions to emigrate. The large majority wants to move “out of Africa”, and the typical potential migrant was found to be young, male, displaying relatively modern values and optimistic about the net benefits of emigration. Signs of positive self-selection were clearly evident in Ghana and Egypt, particularly among women. However, negative self-selection was apparent among Moroccan men. The network effects of potential migrants were found to be fairly important in Ghana and Egypt, but in Senegal and Morocco, such ties play no role in triggering emigration intentions.