Valuing a Beach Day with a Repeated Nested Logit Model of Participation, Site Choice, and Stochastic Time Value

Beach recreation values are often needed by policy-makers and resource managers to efficiently manage coastal resources, especially in popular coastal areas like Southern California. This article presents welfare values derived from random utility maximization-based recreation demand models that explain an individual’s decisions about whether or not to visit a beach and which beach to visit. The models utilize labor market decisions to reveal each individual’s opportunity cost of recreation time. The value of having access to the beach in San Diego County is estimated to be between $21 and$23 per day.Recreation demand, repeated nested logit, labor supply, opportunity cost of leisure, time, beach recreation., Demand and Price Analysis, Environmental Economics and Policy, Institutional and Behavioral Economics, Q26, J22, Q51.,

ESTIMATING THE OPPORTUNITY COST OF RECREATION TIME IN AN INTEGRABLE 2-CONSTRAINT COUNT DEMAND MODEL

How researchers treat the opportunity cost of time substantially influences recreation demand parameter and welfare estimates. This paper presents a utility-theoretic and implementable approach, estimating the shadow value of time jointly with recreation demands for coastal activities, using a generalization of the semilog demand system in a two-constraint model.Consumer/Household Economics, Demand and Price Analysis,

Informed consent comprehension in African research settings

ObjectivePrevious reviews on participants' comprehension of informed consent information have focused on developed countries. Experience has shown that ethical standards developed on Western values may not be appropriate for African settings where research concepts are unfamiliar. We undertook this review to describe how informed consent comprehension is defined and measured in African research settings.MethodsWe conducted a comprehensive search involving five electronic databases: Medline, Embase, Global Health, EthxWeb and Bioethics Literature Database (BELIT). We also examined African Index Medicus and Google Scholar for relevant publications on informed consent comprehension in clinical studies conducted in sub-Saharan Africa. 29 studies satisfied the inclusion criteria; meta-analysis was possible in 21 studies. We further conducted a direct comparison of participants' comprehension on domains of informed consent in all eligible studies.ResultsComprehension of key concepts of informed consent varies considerably from country to country and depends on the nature and complexity of the study. Meta-analysis showed that 47% of a total of 1633 participants across four studies demonstrated comprehension about randomisation (95% CI 13.9–80.9%). Similarly, 48% of 3946 participants in six studies had understanding about placebo (95% CI 19.0–77.5%), while only 30% of 753 participants in five studies understood the concept of therapeutic misconception (95% CI 4.6–66.7%). Measurement tools for informed consent comprehension were developed with little or no validation. Assessment of comprehension was carried out at variable times after disclosure of study information. No uniform definition of informed consent comprehension exists to form the basis for development of an appropriate tool to measure comprehension in African participants.ConclusionsComprehension of key concepts of informed consent is poor among study participants across Africa. There is a vital need to develop a uniform definition for informed consent comprehension in low literacy research settings in Africa. This will be an essential step towards developing appropriate tools that can adequately measure informed consent comprehension. This may consequently suggest adequate measures to improve the informed consent procedure.ObjectifLes normes éthiques élaborées selon les valeurs occidentales ne sont peut-être pas appropriées au contexte africain où les concepts de recherche ne sont pas familiers. Cette revue décrit comment la compréhension du consentement éclairé est définie et mesurée dans les cadres de recherche africains.MéthodesDes recherches ont été effectuées sur Medline, Embase, Global Health, EthxWeb, base de données de la Bioéthique Littérature, Index Medicus African et Google Scholar pour des publications pertinentes sur la compréhension du consentement éclairé dans les études cliniques menées en Afrique sub-saharienne. 29 études répondaient aux critères d'inclusion; une méta-analyse a été possible pour 21 études. La compréhension des participants sur les domaines du consentement éclairé dans toutes les études admissibles a été comparée directement.RésultatsLa compréhension des concepts clés du consentement éclairé varie considérablement selon les pays et dépend de la nature et de la complexité de l’étude. La méta-analyse a montré que 47% des participants ont compris la randomisation (IC95%: 13,9 - 80,9%), 48% ont compris le placebo (IC95%: 19,0 - 77,5%), 30% ont compris le concept de méprise thérapeutique (IC95%: 4,6 - 66,7%). Les outils de mesure de la compréhension du consentement éclairé étaient développés avec peu ou pas de validation.ConclusionsLa compréhension des concepts clés du consentement éclairé est faible en Afrique. Il y a une nécessité vitale d’élaborer une définition uniforme pour la compréhension du consentement éclairé dans les cadres de recherche avec un faible niveau d'alphabétisation en Afrique.ObjetivoLos estándares éticos desarrollados basándose en valores occidentales podrían no ser apropiados para emplazamientos Africanos en donde los conceptos de investigación no son familiares. En esta revisión se describe como la comprensión del consentimiento informado se define y mide en un centro de investigación Africano.MétodosSe buscaron publicaciones relevantes sobre la comprensión del consentimiento informado en estudios clínicos en África subsahariana en Medline, Embase, Global Health, EthxWeb, Bioethics Literature Database, African Index Medicus y Google Scholar. 29 estudios satisfacían los criterios de inclusión y el metaanálisis era posible para 21. La comprensión del consentimiento informado por parte de los participantes se comparó directamente en todos los estudios elegibles.ResultadosLa comprensión de conceptos claves del consentimiento informado varió de forma considerable entre países, y dependía de la naturaleza y de la complejidad del estudio. El meta-análisis mostró que un 47% entendía la aleatorización (IC 95% 13.9-80.9%); un 48% entendía el placebo (IC 95% 19.0-77.5%); y un 30% entendió el concepto terapéutico errado (IC 95% 4.6-66.7%). Las herramientas para medir la comprensión del consentimiento informado se desarrollaron con poca o ninguna validación.ConclusionesEn África, la comprensión de conceptos claves del consentimiento informado es pobre. Existe una necesidad vital de desarrollar una definición uniforme para la comprensión del consentimiento informado en lugares con bajos niveles de alfabetización en África

Thermal and Fragmentation Properties of Star-forming Clouds in Low-metallicity Environments

The thermal and chemical evolution of star-forming clouds is studied for different gas metallicities, Z, using the model of Omukai (2000), updated to include deuterium chemistry and the effects of cosmic microwave background (CMB) radiation. HD-line cooling dominates the thermal balance of clouds when Z \~ 10^{-5}-10^{-3} Z_sun and density ~10^{5} cm^{-3}. Early on, CMB radiation prevents the gas temperature to fall below T_CMB, although this hardly alters the cloud thermal evolution in low-metallicity gas. From the derived temperature evolution, we assess cloud/core fragmentation as a function of metallicity from linear perturbation theory, which requires that the core elongation E := (b-a)/a > E_NL ~ 1, where a (b) is the short (long) core axis length. The fragment mass is given by the thermal Jeans mass at E = E_NL. Given these assumptions and the initial (gaussian) distribution of E we compute the fragment mass distribution as a function of metallicity. We find that: (i) For Z=0, all fragments are very massive, > 10^{3}M_sun, consistently with previous studies; (ii) for Z>10^{-6} Z_sun a few clumps go through an additional high density (> 10^{10} cm^{-3}) fragmentation phase driven by dust-cooling, leading to low-mass fragments; (iii) The mass fraction in low-mass fragments is initially very small, but at Z ~ 10^{-5}Z_sun it becomes dominant and continues to grow as Z is increased; (iv) as a result of the two fragmentation modes, a bimodal mass distribution emerges in 0.01 0.1Z_sun, the two peaks merge into a singly-peaked mass function which might be regarded as the precursor of the ordinary Salpeter-like IMF.Comment: 38 pages, 16 figures, ApJ in pres

Nonlinear viscoelasticity of metastable complex fluids

Many metastable complex fluids such as colloidal glasses and gels show distinct nonlinear viscoelasticity with increasing oscillatory-strain amplitude; the storage modulus decreases monotonically as the strain amplitude increases whereas the loss modulus has a distinct peak before it decreases at larger strains. We present a qualitative argument to explain this ubiquitous behavior and use mode coupling theory (MCT) to confirm it. We compare theoretical predictions to the measured nonlinear viscoelasticity in a dense hard sphere colloidal suspensions; reasonable agreement is obtained. The argument given here can be used to obtain new information about linear viscoelasticity of metastable complex fluids from nonlinear strain measurements.Comment: 7 pages, 3 figures, accepted for publication in Europhys. Let