The project coordinator's problem

A project coordinator has a set of activities with known durations and values which are available for scheduling within a given horizon. There may be both precedence and corequisite restrictions (two activities are corequisites if scheduling one implies the other must be scheduled). The project coordinator's problem is to select the activities to be scheduled, and their start times, so as to maximize the net value of the project when there is no penalty for failing to schedule an activity. An efficient solution procedure is developed and illustrated and several generalizations are discussed.     

America's baby boom generation: the fateful bulge

From 1955-64 nearly 42 million births occurred in the U.S., an unprecedented expansion. The roots of the baby boom lie in the universal rush to early marriage and favorable economic climate for the relatively scarce young men born of the Depression cohort. The impact of the boom interrupted a century-long fertility decline. Pro-marriage, pronatalist norms were revived by the Depression cohort who formed families of at least 2 children or more. During the 1960-70's schools, colleges, and universities were built to accomodate the boom and are now excessive for the baby bust cohort. Unemployment and crime rates rose and fell with the passing of the boom babies through late adolescence and early adulthood. In the 1980's, boom babies will be aged 20-30. Demands for housing will be high. Annual birth numbers will increase even if the rate of childbearing hovers below replacement level at about 1.8 per woman. Per capita earnings and overall labor productivity should improve as the boom baby cohort reaches middle age in the 1990s. However, chances for advancement will be fewer. As the cohort reaches retirement age, the over 65 population will double from 31 million in 2000 to almost 60 million in 2030. Although the burden will be somewhat offset by reduced proportions of under 18-year-olds, the ratio of active workers paying Social Security will fall drastically.     

U.S. population in the 21st century: Which scenario is reasonable?

A major Census Bureau study released in January 1989 has evoked renewed warnings in the media and among some population analysts that the U.S. faces population decline in the next century if it does not increase fertility and/or raise immigration. The report's middle scenario rests on an assumed future total fertility rate (TFR) of 1.8, life expectancy of 81.2 years, and net immigration of 500,000 annually. These mid-range assumptions would yield a United States population of 268 million by 2000, peaking at 302 million in 2040 and falling to 292 million by 2080. Questionable assumptions in the report's most likely scenario are discussed. These are:

1. that immigrants bear children at the same rate as their equivalent age and racial group in the United States population.
2. that the high TFR of Hispanics will not raise the overall 1.8 TFR foreseen for whites as the Hispanic proportion of the white population continues to grow.
3. that net yearly immigration will fall to 575,000 in 1990 and 500,000 by 2000. The Census Bureau's "high" assumption of 800,000 net yearly may be more realistic.

The report's low growth scenario projects future population size that is more reassuring than alarming: 264 million in 2000, rising to 288 million in 2030, and falling to 266 million in 2080. Thus, in ninety years the United States would still have 20 million more people than now. While some fear that such slow growth will lower United States influence and bring labor shortages and an aging population, the nation's quality of life would be less at risk with a population of 266 million than with one approaching the one-half billion projected by the Census report's high estimates.     

The three R's: Residence,religion, and reproduction

Survey research data collected in Rhode Island over a three year interval are used to test six propositions: 1) Suburbanites have higher family size than central city residents. 2) Any differences in family size between Catholics and non-Catholics are larger in central city than in suburban areas. 3) Within religious categories, suburbanites attend church more regularly. 4) Among Catholics, suburban residence is associated with less frequent Communion reception. 5) Among Catholics, church attendance frequency is positively associated with family size. Among non-Catholics no relationship exists. 6) The frequency with which Catholics receive Communion is more strongly associated positively with family size than is church attendance frequency. Propositions 1, 2 and 5 are rejected. Propositions 4 and 6 are accepted. Proposition 3 is accepted for non-Catholics only.     

Population change in Meso-America: The Tip of the demographic Iceberg

This paper examines the demographic situation in Mexico and Central America (Meso-America) and looks at the momentum for growth implied by recent population shifts. Despite successes in reducing fertility levels in many Meso-American countries, the dramatic declines in mortality among infants and children have given rise to a "death dearth" that is contributing to a new "baby boom" in these countries; thus our subtitle, "The Tip of the Iceberg."The impacts of such population growth on education, the economy and migration are considered in some detail. The anticipated inability of country economies to provide jobs for the thousands of young adults entering the labor force in future years could result in significant increases in the number seeking to migrate in a northerly direction. Thus, the United States is also vitally interested in the demographic shifts taking place south of its border.The need for a more unified regional approach to some of the social and economic problems facing these nations is pointed out as is the need for a more rational immigration policy on the part of the United States in light of the potential increase in immigration in future years.