A self-validating numerical method for computation of central and non-central F probabilities and percentiles

A self-validating numerical method based on interval analysis for the computation of central and non-central F probabilities and percentiles is reported. The major advantage of this approach is that there are guaranteed error bounds associated with the computed values (or intervals), i.e. the computed values satisfy the user-specified accuracy requirements. The methodology reported in this paper can be adapted to approximate the probabilities and percentiles for other commonly used distribution functions.     

Missing the Target? Correspondence of Fertility Intentions and Behavior in the U.S.

Building on a framework suggested by Bongaarts (2001)and using data from the 1979 National LongitudinalSurvey of Youth, we describe the correspondencebetween intended family size and observed fertilityfor the 1957 to 1961 birth cohorts of U.S. women andmen. Over an 18-year period (1982–2000), we showthat while aggregate intentions are quite stable,discrepancies are very common at the individual level.Women and men were more likely to err in predictingnumber of additional births in the period 1982–2000 thanto hit their target number. A very strong predictor of over-and underachieving fertility is initial intended parity. Thosewho intended more than two children tended to have fewerchildren than intended, while those who intended fewer thantwo children tended to have more children than intended. Inaddition and consistent with life course arguments, thoseunmarried in 1982, childless in 1982, and (for women) stillin school in 1982 were most likely to underachieve their 2000intended parity (i.e., have fewer children than intended). Weconclude by reflecting on how the circumstances that allowdiscrepancies between intentions and behavior to almost``balance'' in the U.S. may cumulate differently elsewhere toproduce much lower fertility.     

Illustration Of Three-Dimensional Surfaces

With the ready availability of computer graphics packages, it is now straightforward to produce isometric projections of three-dimensional surfaces. The usefulness of such projections is shown by means of a number of examples. Illustrating likelihood surfaces and bivariate density functions.     

Cell Proliferation and Formaldehyde-Induced Respiratory Carcinogenesis

Formaldehyde is a nasal carcinogen in the rat but the cancer risk this chemical poses for humans remains to be determined. Formaldehyde induces nonlinear, concentration-dependent increases in nasal epithelial cell proliferation and DNA-protein cross-link formation following short-term exposure. Presented in this review are results from a mechanistically based formaldehyde inhalation study in which an important endpoint was the measurement of cell proliferation indices in target sites for nasal tumor induction. Male Fischer 344 rats were exposed to 0, 0.7, 2, 6, 10, or 15 ppm formaldehyde for up to 2 years (6 hr/day, 5 day/week). Statistically significant increases in cell proliferation were confined to the 10 and 15 ppm groups, which remained elevated throughout the study. The concentration-dependent increases in cell proliferation correlated strongly with the tumor response curve, supporting the proposal that sustained increases in cell proliferation are an important component of formaldehyde carcinogenesis. The nonlinearity observed in formaldehyde-induced rodent nasal cancer is consistent with a high-concentration effect of regenerative cell proliferation of the target organ coupled with the genotoxic effects of formaldehyde. Cell kinetic data from these studies provide important information that may be utilized in the assessment of risk for humans exposed to formaldehyde.     

An interview with W. H. Hutt

W. H. Hutt is 85 years old and is one of the most important economists of this century. That this is too little appreciated is largely because his academic career did not take place in his native England. Instead, in 1928, after a short career in publishing, the graduate of the London School of Economics set sail for South Africa and the University of Cape Town. During his 37 years there, Professor Hutt produced an impressive body of work, some of which have become classics among his devotees, includingThe Theory of Collective Bargaining (1930),Economists and the Public (1936),The Theory of Idle Resources (1939),Plan for Reconstruction (1943),Keynesianism — Retrospect & Prospect (1963), andThe Economics of the Colour Bar (1964). Hutt came to the United States in December 1965 to serve as a visiting professor at the University of Virginia, and has served in a similar capacity at many American universities. While in the United States Hutt has produced such works asThe Strike-Threat System (1973),A Rehabilitation of Say’s Law (1975), andThe Keynesian Episode (1979). Professor Hutt currently is Emeritus Visiting Professor of Economics at the University of Dallas and he continues to work on an autobiography and a new book, tentatively titledLabor’s Disadvantage.     

Risk Characterization of Methyl tertiary Butyl Ether (MTBE) in Tap Water

Methyl tertiary butyl ether (MTBE) can enter surface water and groundwater through wet atmospheric deposition or as a result of fuel leaks and spills. About 30% of the U.S. population lives in areas where MTBE is in regular use. Ninety-five percent of this population is unlikely to be exposed to MTBE in tap water at concentrations exceeding 2 ppb, and most will be exposed to concentrations that are much lower and may be zero. About 5% of this population may be exposed to higher levels of MTBE in tap water, resulting from fuel tank leaks and spills into surface or groundwater used for potable water supplies. This paper describes the concentration ranges found and anticipated in surface and groundwater, and estimates the distribution of doses experienced by humans using water containing MTBE to drink, prepare food, and shower/bathe. The toxic properties (including potency) of MTBE when ingested, inhaled, and in contact with the skin are summarized. Using a range of human toxic potency values derived from animal studies, margins of exposure (MOE) associated with alternative chronic exposure scenarios are estimated to range from 1700 to 140,000. Maximum concentrations of MTBE in tap water anticipated not to cause adverse health effects are determined to range from 700 to 14,000 ppb. The results of this analysis demonstrate that no health risks are likely to be associated with chronic and subchronic human exposures to MTBE in tap water. Although some individuals may be exposed to very high concentrations of MTBE in tap water immediately following a localized spill, these exposures are likely to be brief in duration due to large-scale dilution and rapid volatilization of MTBE, the institution of emergency response and remediation measures to minimize human exposures, and the low taste and odor thresholds of MTBE which ensure that its presence in tap water is readily detected at concentrations well below the threshold for human injury.