Vertical foodweb structure of freshwater zooplankton assemblages estimated by stable nitrogen isotopes

Although theoretical foodweb models predict the presence of only three to four trophic categories, estimation of “potential” vertical foodweb structure from species lists and inferred feeding interactions suggest that as many as 7 trophic categories can occur in the pelagic foodwebs of North American glaciated lakes. A compilation of data on the nitrogen isotopic composition of zooplankton from 46 Canadian Shield lakes suggested the average existence of one “realized” trophic category in addition to that of filter-feeding, herbivorous cladocerans. When phytoplankton, planktivorous invertebrates, and plantivorous and piscivorous fish are included, the vertical foodweb structure in the pelagic zones of these lakes are greater than those hypothesized from some theoretical models.     

Welfare benefits and birth decisions of never-married women

For some time now, the out-of-wedlock birthrate has been increasing rapidly in the United States. This has prompted several states to propose (and in some cases, enact) legislation to deny access to higher AFDC benefits for families in which the mother gives birth while receiving AFDC. The authors investigate whether AFDC benefit levels are systematically related to the family-size decisions of never-married women. Using a bivariate probit model with state and time fixed effects, applied to Current Population Survey data for the years 1980–1988, it is found that the basic benefit level for a family of two (one adult and one child) and the incremental benefit for a second child positively affects the family size decisions of black and Hispanic women, but not of white women. The effects are concentrated among high school dropouts (no effects are found for high school graduates). The authors conclude that rather than to uniformly deny benefits to all AFDC women that bear children, a better targeted policy might be to alter the AFDC benefit structure in such a way as to encourage single mothers to complete high school. However, being a high school dropout might be a proxy for some other underlying characteristic of the woman, and encouraging women to complete high school who otherwise would not might have no effect whatsoever on nonmarital births.     

Demography of disaster: Population estimates after hurricane Andrew

Hurricane Andrew blasted through the southern tip of Florida in August 1992, damaging or destroying tens of thousands of homes and forcing hundreds of thousands of persons to move at least temporarily to different places of residence. The hurricane not only disrupted the lives of many Floridians, but destroyed the statistical basis for producing local population estimates in South Florida as well. These estimates are used for many types of decision-making, from the distribution of state revenue-sharing dollars to choosing sites for fast-food restaurants. This article describes the estimation problems created by the hurricane and how those problems were resolved through the use of existing data sources and the collection of new types of data. It closes with a discussion of several conceptual, methodological and procedural issues that will have to be faced in virtually any attempt to estimate the demographic consequences of natural disasters.An earlier version of this paper was presented at the 1994 annual meeting of the Population Association of America, Miami, Florida, USA.     

Lactation and fertility in Rural Bangladesh

Summary Analysis of data from various phases of a study of post-partum amenorrhoea in Bangladesh illustrated good aggregate consistency of response on menstrual status, but less individual consistency on duration of post-partum amenorrhoea. Using life table techniques, the median duration of amenorrhoea was calculated as 19.9 months for women with births between February and September 1974. There were substantial seasonal variations in duration, with the median decreasing from 21.5 months for women with February births to 16.9 months for those with September births. By contrast, the median duration of post-partum amenorrhoea varies by only two months for women in the lowest and highest quartiles of weight and weight for height. The seasonal pattern was similar for all weight groups.     

Some new techniques for applying the housing unit method of local population estimation

The housing unit method of population estimation is often characterized as being imprecise and having an upward bias. We believe that the method itself cannot properly be characterized by a particular level of precision or direction of bias. Only specific techniques of applying the method can have such characteristics. In this paper we discuss several new techniques we have developed for estimating households and the average number of persons per household. Estimates produced by these techniques are compared to estimates produced by several other techniques. Special census results from Florida provide preliminary evidence that the new techniques produce more precise, less biased estimates than the other techniques.     

The Swiss Equal Rights Amendment: A case study

In June, 1981, the Swiss passed a constitutional amendment providing legal equality for men and women. How that could happen in a legal system that appears to be more than most designed to maintain male privilege is the major topic of this case study. The nature of the political system into which the Swiss equal rights amendment was introduced and of the support and opposition to the amendment are examined. The impact of the amendment since its passage is reported. Each major aspect of the Swiss situation is compared with the American experience with the Equal Rights Amendment and the significance of the Swiss case for American social action is delineated.Richard Kerckhoff is Professor of Family Studies and Timothy Leupp is a graduate student in the Department of Child Development and Family Studies. The study reported here was made possible by time and resources provided by Purdue University, School of Consumer and Family Sciences.     

Are old-age security and the utility of children in rural India really unimportant?

Abstract Extract In their recent paper in this journal M. and Carol Vlassoff are to be commended for helping to remedy the dearth of empirical studies on the old-age security motive for children (and particularly sons) in rural areas of developing countries.(1) However, while the questionnaire which they applied to 357 ever-married men in a rural village in Maharashtra state in India is potentially useful, several of the conclusions they derive from it are unwarranted and, if left unquestioned, would undoubtedly have the effect of setting back the serious investigation of the effects of this motive rather than furthering it. The invalid or at least questionable inferences are taken up one at a time in the order of their appearance:     

Development of a social monitoring system at the local level: An experiment in the Southern Region of the Democratic Republic of Sudan

Subjective indicators of life quality are used frequently in the planning and decision making process. The limitations inherent in the use of subjective indicators often go unnoticed among those most likely to use such data in the context of planned change. We direct attention to a potential source of error in subjective evaluations of community services and facilities. Specifically, we utilize repeated measures to test for response bias that results from placing items in alternative sections of the same survey instrument. Evidence concerning the hypothesized presence of systematic bias was mixed. When overall service evaluation items were embedded within a section devoted exclusively to that service, considerable systematic bias was observed. The findings indicate that the choice of question format depends upon the ultimate use to which the data will be put.