William D. White

Element transport from slab to volcanic front at the Mariana arc

We present a comprehensive geochemical data set for the most recent volcanics from the Mariana Islands, which provides new constraints on the timing and nature of fluxes from the subducting slab. The lavas display many features typical of island arc volcanics, with all samples showing large negative niobium anomalies and enrichments in alkaline earth elements and lead (e.g., high Ba/La and Pb/Ce). Importantly, many of these key ratios correlate with a large range in 238U excesses, (238U/230Th) = 0.97–1.56. Geochemical features show island to island variations; lavas from Guguan have the largest 238U-excesses, Pb/Ce and Ba/La ratios, while Agrigan lavas have small 238U excesses, the least radiogenic 143Nd/144Nd, and the largest negative cerium and niobium anomalies. These highly systematic variations enable two discrete slab additions to the subarc mantle to be identified. The geochemical features of the Agrigan lavas are most consistent with a dominant subducted sediment contribution. The added sedimentary component is not identical to bulk subducted sediment and notably shows a marked enrichment of Th relative to Nb. This is most readily explained by melt fractionation of the sediment with residual rutile and transfer of sedimentary material as a melt phase. For most of the highly incompatible elements, the sedimentary contribution dominates the total elemental budgets of the lavas. The characteristics best exemplified by the Guguan lavas are attributed to a slab-derived aqueous fluid phase, and Pb and Sr isotope compositions point toward the subducted, altered oceanic crust as a source of this fluid. Variable addition of the sedimentary component, but near-constant aqueous fluid flux along arc strike, can create the compositional trends observed in the Mariana lavas. High field strength element ratios (Ta/Nb and Zr/Nb) of the sediment poor Guguan lavas are higher than those of most mid-oceanic ridge basalts and suggest a highly depleted subarc mantle prior to any slab additions. The 238U-230Th systematics indicate >350 kyr between sediment and mantle melting but <30 kyr between slab dehydration and eruption of the lavas. This necessitates rapid magma migration rates and suggests that the aqueous fluid itself may trigger major mantle melting.

Os isotope systematics in ocean island basalts

New ReOs isotopic results for Os-poor basalts from St. Helena, the Comores, Samoa, Pitcairn and Kerguelen dramatically expand the known range of initial 186Os/187Os ratios in OIBs to values as high as 1.7. In contrast to the Os isotopic uniformity of Os-rich basalts from the HIMU islands of Tubuai and Mangaia found by Hauri and Hart [1], our values for St. Helena span most of the known range of Os isotopic variability in oceanic basalts (initial 187Os/186Os ranges from 1.2 to 1.7). Generation of such radiogenic Os in the mantle requires melting of source materials that contain large proportions of recycled oceanic crust. The very low Os concentrations of most of the basalts analyzed here, however, leave them susceptible to modification via interaction with materials containing radiogenic Os in the near-surface environment. Thus the high 186Os/187Os ratios may result from assimilation of radiogenic Os-rich marine sediments, such as Mn oxides, within the volcanic piles traversed by these magmas en route to the surface. Furthermore, the Os isotopic signatures of Os-rich, olivine-laden OIBs may reflect the accumulation of lithospheric olivine, rather than simply their mantle source characteristics. The extent to which these processes alter the view of the mantle obtained via study of ReOs systematics in oceanic basalts is uncertain. These effects must be quantified before ReOs systematics in OIBs can be used with confidence to investigate the nature of mantle heterogeneity and its causes.

Price and Concentration in Hospital Markets: The Switch from Patient-Driven to Payer-Driven Competition

PERHAPS the most widely accepted paradigm of industrial organization (I/O) is that competition lowers prices or, alternatively, that price/cost margins are lower in less concentrated markets.1 The applicability of this paradigm for hospital markets has been questioned. For example, in United States vs. Carilion Health System and Roanoke Valley Hospital, the district and appellate courts accepted evidence that hospital prices are lower in more concentrated markets and thereby approved a merger between the two largest hospitals in a three-hospital market.2 The view that competition has a weak or perverse effect on hospital prices is shared by a number of researchers,3 is a common theme in newspaper stories

Determinants of managed care penetration

This paper examines factors associated with differences in managed care penetration across geographic areas. Two alternative measures of managed care penetration are considered: the percentage of revenue physicians received from managed care contracts and market survey data on enrollments in managed care plans. Results are similar for both types of measures. Our analysis suggests that demographics, labor market characteristics and supply side variables including the level of concentration in hospital markets, hospital occupancy rates and the practice organization patterns of physicians are all important determinants of managed care penetration.

Is Managed Care Leading to Consolidation in Health-care Markets?

OBJECTIVE To determine the extent to which managed care has led to consolidation among hospitals and physicians. DATA SOURCES We use data from the American Hospital Association, American Medical Association, and government censuses. STUDY DESIGN Two stage least squares regression analysis examines how cross-section variation in managed care penetration affects provider consolidation, while controlling for the endogeneity of managed-care penetration. Specifically, we examine inpatient hospital markets and physician practice size in large metropolitan areas. DATA COLLECTION METHODS All data are from secondary sources, merged at the level of the Primary Metropolitan Statistical Area. PRINCIPAL FINDINGS We find that higher levels of local managed-care penetration are associated with substantial increases in consolidation in hospital and physician markets. In the average market (managed-care penetration equaled 34 percent in 1994), managed care was associated with an increase in the Herfindahl of .054 between 1981 and 1994, moving from .096 in 1981 to .154. This is equivalent to moving from 10.4 equal-size hospitals to 6.5 equal-sized hospitals. In the physician market place, we estimate that at the mean, managed care resulted in a 14 percentage point decrease of physicians in solo practice between 1986 and 1995. This implies a decrease in the percentage of doctors in solo practice from 38 percent in 1986 to 24 percent by 1995.

Illegitimate magmas of the Galápagos: Insights into mantle mixing and magma transport

Roughly 1–2% of the flows erupted from flank vents of the western Galapagos shield volcanoes have anomalous compositions. We call these illegitimate magmas because of their uncertain parentage. Because some illegitimate magmas are compositionally indistinguishable from lavas of an adjacent volcano and erupt from the flank facing the adjacent volcano, such magmas apparently result from lateral intrusion of magma from the adjacent volcano. Other illegitimate magmas come from parts of the Galapagos plume that have incompletely mixed or result from unusually advanced melting of part of the mantle.

The impact of occupational licensure of clinical laboratory personnel.

This paper develops a model of the economic impact of occupational licensure. The model is then used to estimate the effects of occupational licensure on wages and the division of labor in clinical laboratories and to generate a low-bound estimate of the welfare impact of licensure. Estimates are based on cross-section and time-series data on areas with and without licensure of laboratory personnel. Recent licensure laws have no effect on wages or employment, but older, more stringent laws sharply increase the wages and employment of skilled personnel in laboratories.

Information and the control of agents

Abstract Standard principal-agent models examine problems with controlling moral hazard under conditions of imperfect information This paper explores whether the ability to costlessly monitor agent/employees within a firm with certainty is a sufficient condition to eliminate problems with control A simple model of employee theft is used to demonstrate that even if theft can always be detected in a timely fashion, problems with control may persist Implications of this finding are discussed.

How Fast Are Hospital Prices Really Rising

The hospital services component of the Consumer Price Index (CPI) measures the cost of hospital services to private patients paying list prices. It is, however, widely used as an estimate of the overall rate of inflation in hospital prices in spite of the fact that there are strong reasons to believe that it is inappropriate to use the CPI for this purpose. This is because: 1) A growing number of patients are enrolled in health maintenance organizations (HMOs) and preferred provider organizations (PPOs), which negotiate discounts from list prices; and 2) the size of the discounts may have been increasing. The potential result is a gap between the rate of inflation of list prices and the rate of inflation of actual prices paid in transactions. This study explores whether such a gap exists and determines its possible magnitude. In addition, parallel indices for list and actual prices are computed on the basis of data from California hospitals for fiscal years 1983-1988. The analysis suggests that list price inflation has greatly exceeded actual inflation—by a factor of two for recent years. These findings have broad implications for evaluating not only inflation but also the impact of cost containment strategies.

Geochemical Earth Reference Model (GERM): description of the initiative

Abstract The Geochemical Earth Reference Model (GERM) initiative is a grass-root effort with the goals of establishing a community consensus on a chemical characterization of the Earth, its major reservoirs, and the fluxes between them. The GERM initiative will provide a review of available scientific constraints for: (1) the composition of all major chemical reservoirs of the present-day Earth, from core to atmosphere; (2) present-day fluxes between reservoirs; (3) the Earths chemical and isotopic evolution since accretion; and (4) the chemical and isotopic evolution of seawater as a record of global tectonics and climate. Even though most of the constraints for the GERM will be drawn from chemical data sets, some data will have to come from other disciplines, such as geophysics, nuclear physics, and cosmochemistry. GERM also includes a diverse chemical and physical data base and computer codes that are useful for our understanding of how the Earth works as a dynamic chemical and physical system. The GERM initiative is developed in an open community discussion on the World Wide Web (http://www-ep.es.llnl.gov/germ/germ-home.html) that is moderated by editors with responsibilities for different reservoirs, fluxes, data bases, and other scientific or technical aspects. These editors have agreed to lay out an initial, strawman GERM for their respective sections and to moderate community discussions leading to a first, preliminary consensus. The development of the GERM began with an initial workshop in Lyon, France in March, 1996. Since then, the GERM has continued to be developed on the Internet, punctuated by workshops and special sessions at professional meetings. A second GERM workshop will be held in La Jolla, CA USA on March 10–13, 1998.