RAND Corporation

About: RAND Corporation is a nonprofit organization based out in Santa Monica, California, United States. It is known for research contribution in the topics: Health care & Population. The organization has 9602 authors who have published 18570 publications receiving 744658 citations.

Does WIC work? The effects of WIC on pregnancy and birth outcomes.

Abstract: Support for WIC, the Special Supplemental Nutrition Program for Women, Infants, and Children, is based on the belief that "WIC works." This consensus has lately been questioned by researchers who point out that most WIC research fails to properly control for selection into the program. This paper evaluates the selection problem using rich data from the national Pregnancy Risk Assessment Monitoring System. We show that relative to Medicaid mothers, all of whom are eligible for WIC, WIC participants are negatively selected on a wide array of observable dimensions, and yet WIC participation is associated with improved birth outcomes, even after controlling for observables and for a full set of state-year interactions intended to capture unobservables that vary at the state-year level. The positive impacts of WIC are larger among subsets of even more disadvantaged women, such as those who received public assistance last year, single high school dropouts, and teen mothers.

Propagation of electromagnetic waves in plasmas

Abstract: Green's function techniques are used to treat the propagation of electromagnetic waves in uniform, weakly interacting plasmas near equilibrium in the absence of external magnetic fields. The frequency and the damping of electromagnetic waves in a medium are related to the local complex conductivity tensor, which is calculated by the diagrammatic techniques of modern field theory. Physical quantities are calculated in terms of a consistent many-particle perturbation expansion in powers of a (weak) coupling parameter. An open-diagram technique is introduced which simplifies the calculation of absorptive parts. For long-wavelength longitudinal waves (i.e., electron plasma oscillations) it is found that the main absorption mechanism in the electron-ion plasma is the two-particle collision process appropriately corrected for collective effects and not the one-particle (or Landau) damping process. Electron-ion collisions produce a damping effect which remains finite for long wavelengths. The effect of electron-electron collisions vanishes in this limit. The absorption of transverse radiation is also considered; calculations for the electron-ion plasma are in essential agreement with the recent work of Dawson and Oberman. The results for the absorptive part of the conductivity tensor for long-wavelength electromagnetic waves in a plasma where the phase velocity $\frac{\ensuremath{\omega}}{k}$ is much greater than the rms particle velocity is for the electron-ion plasma: $4\ensuremath{\pi} \mathrm{Im}{\ensuremath{\sigma}}_{\mathrm{ij}}(\mathbf{k},\ensuremath{\omega})=\frac{{\ensuremath{\Omega}}_{p}}{6\sqrt{2}{\ensuremath{\pi}}^{\frac{3}{2}}}\frac{\ensuremath{\Omega}_{p}^{}{}_{}{}^{2}}{{\ensuremath{\omega}}^{2}}\frac{k_{D}^{}{}_{}{}^{2}}{n}\mathrm{ln}\left(\frac{{C}_{a}(\ensuremath{\omega})}{\ensuremath{\beta}\ensuremath{\hbar}\ensuremath{\omega}}\right){\ensuremath{\delta}}_{\mathrm{ij}}$ where $\ensuremath{\Omega}_{p}^{}{}_{}{}^{2}=4\ensuremath{\pi}{e}^{2}n{m}^{\ensuremath{-}1}$, $k_{D}^{}{}_{}{}^{2}=4\ensuremath{\pi}{e}^{2}n\ensuremath{\beta}$, and $\ensuremath{\beta}={(\mathrm{kT})}^{\ensuremath{-}1}$. The effects of dynamic screening are entirely contained in definite integral ${C}_{a}(\ensuremath{\omega})$ which is numerically evaluated. The calculations are valid for temperatures and densities which satisfy the inequalities: ${(\frac{4\ensuremath{\pi}{e}^{2}n}{m})}^{\frac{3}{2}}{(\frac{\ensuremath{\hbar}}{\mathrm{kT}})}^{3}\ensuremath{\ll}{(\frac{4\ensuremath{\pi}{e}^{2}n}{\mathrm{kT}})}^{\frac{3}{2}}{n}^{\ensuremath{-}1}\ensuremath{\ll}{(\frac{4\ensuremath{\pi}{e}^{2}n}{m})}^{\frac{1}{2}}(\frac{\ensuremath{\hbar}}{\mathrm{kT}})\ensuremath{\ll}1.$ Reading from left to right these inequalities justify the use of Boltzmann statistics, the Born approximation, and the neglect of wave mechanical interference effects. The weak-coupling approximation is justified by ${(\frac{4\ensuremath{\pi}{e}^{2}n}{\mathrm{kT}})}^{\frac{3}{2}}{n}^{\ensuremath{-}1}\ensuremath{\ll}1$. These restrictions are satisfied, for example, if $Tg{10}^{6}$ \ifmmode^\circ\else\textdegree\fi{}K and $nl{10}^{20}$ particles/${\mathrm{cm}}^{3}$. For these hot plasmas a natural short-wavelength cutoff appears at roughly the thermal de Broglie wavelength. Electrons and ions are found to produce comparable screening effects. To illustrate the application of these techniques to degenerate, low-temperature systems, the absorption process in a high-density electron gas is briefly considered.

Substance use Trajectories from Early Adolescence to Emerging Adulthood: A Comparison of Smoking, Binge Drinking, and Marijuana use:

Abstract: Over the past several years, there has been growing interest in identifying distinct developmental trajectories of substance use. Using data from the RAND Adolescent/Young Adult Panel Study (N = 6,527), we synthesize our prior findings on patterns of smoking, binge drinking, and marijuana use from early adolescence (age 13) to emerging adulthood (age 23). We also present new data on how these trajectory classes compare on key psychosocial and behavioral outcomes during emerging adulthood. For each type of substance use, we found two periods of vulnerability: early adolescence and the transition to emerging adulthood. As expected, early users were at relatively high risk for poor outcomes at age 23 compared to consistent low-level users and abstainers, even if they reduced their use during adolescence. However, youths who were not early users, but steadily increased their use over time, also tended to be at relatively high risk. Results suggest that multiple prevention approaches might be needed to success...

Prevalence of child and adolescent exposure to community violence

Abstract: Emerging as one of the most significant health issues facing American youth today, child and adolescent exposure to community violence has generated much interest across multiple disciplines. Most research to date has focused on documenting the prevalence of community violence and the emotional and behavioral ramifications. This paper provides an overview of the current literature regarding prevalence of youth exposure to community violence, and identifies those areas where further research is warranted. In addition to examining overall rates of community violence exposure, this paper reviews the prevalence of different types of community violence, such as weapon use, physical aggression, and crime-related events. Predictors of community violence exposure, including gender, age, race, socioeconomic status, behavior patterns, and geography, are discussed.

Disparate prevalence estimates of PTSD among service members who served in Iraq and Afghanistan: possible explanations.

Abstract: The authors reviewed 29 studies that provide prevalence estimates of posttraumatic stress disorder (PTSD) among service members previously deployed to Operations Enduring and Iraqi Freedom and their non-U.S. military counterparts. Studies vary widely, particularly in their representativeness and the way PTSD is defined. Among previously deployed personnel not seeking treatment, most prevalence estimates range from 5 to 20%. Prevalence estimates are generally higher among those seeking treatment: As many as 50% of veterans seeking treatment screen positive for PTSD, though much fewer receive a PTSD diagnosis. Combat exposure is the only correlate consistently associated with PTSD. When evaluating PTSD prevalence estimates among this population, researchers and policymakers should carefully consider the method used to define PTSD and the population the study sample represents.