Recent Empirical Studies (recent + empirical_studies)

Distribution by Scientific Domains


Selected Abstracts


A sparse marker extension tree algorithm for selecting the best set of haplotype tagging single nucleotide polymorphisms

GENETIC EPIDEMIOLOGY, Issue 4 2005
Ke Hao
Abstract Single nucleotide polymorphisms (SNPs) play a central role in the identification of susceptibility genes for common diseases. Recent empirical studies on human genome have revealed block-like structures, and each block contains a set of haplotype tagging SNPs (htSNPs) that capture a large fraction of the haplotype diversity. Herein, we present an innovative sparse marker extension tree (SMET) algorithm to select optimal htSNP set(s). SMET reduces the search space considerably (compared to full enumeration strategy), and therefore improves computing efficiency. We tested this algorithm on several datasets at three different genomic scales: (1) gene-wide (NOS3, CRP, IL6 PPARA, and TNF), (2) region-wide (a Whitehead Institute inflammatory bowel disease dataset and a UK Graves' disease dataset), and (3) chromosome-wide (chromosome 22) levels. SMET offers geneticists with greater flexibilities in SNP tagging than lossless methods with adjustable haplotype diversity coverage (,). In simulation studies, we found that (1) an initial sample size of 50 individuals (100 chromosomes) or more is needed for htSNP selection; (2) the SNP tagging strategy is considerably more efficient when the underlying block structure is taken into account; and (3) htSNP sets at 80,90% , are more cost-effective than the lossless sets in term of relative power, relative risk ratio estimation, and genotyping efforts. Our study suggests that the novel SMET algorithm is a valuable tool for association tests. Genet. Epidemiol. 29:336,352, 2005. © 2005 Wiley-Liss, Inc. [source]


Efficacy beliefs predict collaborative practice among intensive care unit nurses

JOURNAL OF ADVANCED NURSING, Issue 3 2010
Pascale M. Le Blanc
le blanc p.m., schaufeli w.b., salanova m., llorens s. & nap r.e. (2010) Efficacy beliefs predict collaborative practice among intensive care unit nurses. Journal of Advanced Nursing66(3), 583,594. Abstract Aim., This paper is a report of an investigation of whether intensive care nurses' efficacy beliefs predict future collaborative practice, and to test the potential mediating role of team commitment in this relationship. Background., Recent empirical studies in the field of work and organizational psychology have demonstrated that (professional) efficacy beliefs are reciprocally related to workers' resources and well-being over time, resulting in a positive gain spiral. Moreover, there is ample evidence that workers' affective commitment to their organization or work-team is related to desirable work behaviours such as citizenship behaviour. Methods., A longitudinal design was applied to questionnaire data from the EURICUS-project. Structural Equation Modelling was used to analyse the data. The sample consisted of 372 nurses working in 29 different European intensive care units. Data were collected in 1997 and 1998. However, our research model deals with fundamental psychosocial processes that are not time-dependent. Moreover, recent empirical literature shows that there is still room for improvement in ICU collaborative practice. Results., The hypotheses that (i) the relationship between efficacy beliefs and collaborative practice is mediated by team commitment and (ii) efficacy beliefs, team commitment and collaborative practice are reciprocally related were supported, suggesting a potential positive gain spiral of efficacy beliefs. Conclusion., Healthcare organizations should create working environments that provide intensive care unit nurses with sufficient resources to perform their job well. Further research is needed to design and evaluate interventions for the enhancement of collaborative practice in intensive care units. [source]


Comparative analysis of three user equilibrium models under stochastic demand

JOURNAL OF ADVANCED TRANSPORTATION, Issue 3 2008
Zhong Zhou
Abstract Recent empirical studies on the value of time and reliability reveal that travel time variability plays an important role on travelers' route choice decision process. It can be considered as a risk to travelers making a trip. Therefore, travelers are not only interested in saving their travel time but also in reducing their risk. Typically, risk can be represented by two different aspects: acceptable risk and unacceptable risk. Acceptable risk refers to the reliability aspect of acceptable travel time, which is defined as the average travel time plus the acceptable additional time (or buffer time) needed to ensure more frequent on-time arrivals, while unacceptable risk refers to the unreliability aspect of unacceptable late arrivals (though infrequent) that have a travel time excessively higher than the acceptable travel time. Most research in the network equilibrium based approach to modeling travel time variability ignores the unreliability aspect of unacceptable late arrivals. This paper examines the effects of both reliability and unreliability aspects in a network equilibrium framework. Specifically, the traditional user equilibrium model, the demand driven travel time reliability-based user equilibrium model, and the ,-reliable mean-excess travel time user equilibrium model are considered in the investigation under an uncertain environment due to stochastic travel demand. Numerical results are presented to examine how these models handle risk under travel time variability. [source]


A METAPOPULATION PERSPECTIVE ON GENETIC DIVERSITY AND DIFFERENTIATION IN PARTIALLY SELF-FERTILIZING PLANTS

EVOLUTION, Issue 12 2002
Pärk. Ingvarsson
Abstract., Partial self-fertilization is common in higher plants. Mating system variation is known to have important consequences for how genetic variation is distributed within and among populations. Selfing is known to reduce effective population size, and inbreeding species are therefore expected to have lower levels of genetic variation than comparable out crossing taxa. However, several recent empirical studies have shown that reductions in genetic diversity within populations of inbreeding species are far greater than the expected reductions based on the reduced effective population size. Two different processes have been argued to cause these patterns, selective sweeps (or hitchhiking) and background selection. Both are expected to be most effective in reducing genetic variation in regions of low recombination rates. Selfing is known to reduce the effective recombination rate, and inbreeding taxa are thus thought to be particularly vulnerable to the effects of hitchhiking or background selection. Here I propose a third explanation for the lower-than-expected levels of genetic diversity within populations of selfing species; recurrent extinctions and recolonizations of local populations, also known as metapopulation dynamics. I show that selfing in a metapopulation setting can result in large reductions in genetic diversity within populations, far greater than expected based the lower effective population size inbreeding species is expected to have. The reason for this depends on an interaction between selfing and pollen migration. [source]


Can circle hook use benefit billfishes?

FISH AND FISHERIES, Issue 2 2009
Joseph E Serafy
Abstract We performed a quantitative review to evaluate circle hook use in recreational and commercial hook-and-line fisheries that interact with billfishes (Family: Istiophoridae). Specifically, we scrutinized the findings of 11 recent empirical studies that reported, on a species-specific basis, side-by-side measures of circle vs. J-hook fishing performance: catch, mortality, deep-hooking and bleeding rates. Of the 30 total comparisons extracted from the literature that satisfied our inclusion criteria, 13 indicated significant differences between hook types for the specific metric compared. No study reported significant billfish catch rate differences between hook types. However, when significant differences between hook types were found, higher mortality rates and higher rates of deep-hooking and bleeding were associated with J-hooks relative to circle hooks. We conclude that empirical evidence is sufficient to promote circle hook use in almost all hook-and-line fishery sectors that typically interact with istiophorids. However, billfish conservation benefits will only be realized if fishers use unmodified circle hooks, commit to releasing live fish and take other appropriate measures which maximize post-release survival. While there may be fishing modes where circle hook effects are negative, for billfish conservation, we recommend managers grant exceptions to circle hook use only when experimental results support such a practice. [source]


Why Not Guns and Butter: Responses to Economic Turmoil

FOREIGN POLICY ANALYSIS, Issue 4 2010
Philip Arena
Diversionary approaches rarely explain why leaders use force in response to economic turmoil rather than addressing the problem directly. Those few studies that do address this often assume leaders can either respond with foreign policy or economic policy, but not both. I develop a formal model in which governments may employ macroeconomic policy tools, enter into an international crisis, or both. The results indicate that the relationship between economic conditions and the decision to use force may be either positive or negative. I discuss the implications with respect to recent empirical studies of the link between economic conditions and international conflict. [source]


Post-Traumatic Stress Disorder in Children: Controversies and Unresolved Issues

JOURNAL OF CHILD AND ADOLESCENT PSYCHIATRIC NURSING, Issue 4 2000
June A. Tierney MSN
TOPIC. Questions regarding hozu severely traumatized children may meet diagnostic criteria for an accurate diagnosis of posttraumatic stress disorder (PTSD), the comorbidity of PTSD zuith many other psychiatric illnesses, and the possibility that PTSD is not a valid diagnostic formulation as it has been applied to children and adolescents demonstrate that the currently held concept of PTSD may not be operationally sound. PURPOSE. To explore recent empirical studies to demonstrate the current state of controversy and postulate future direction of the conceptual framework. SOURCES. Selected published literature. CONCLUSIONS. PTSD in children and adolescents, as it is popularly understood as a conceptual framework, is found to be undergoing a conceptual metamorphosis. [source]


Molecular ecology of social behaviour: analyses of breeding systems and genetic structure

MOLECULAR ECOLOGY, Issue 2 2001
Kenneth G. Ross
Abstract Molecular genetic studies of group kin composition and local genetic structure in social organisms are becoming increasingly common. A conceptual and mathematical framework that links attributes of the breeding system to group composition and genetic structure is presented here, and recent empirical studies are reviewed in the context of this framework. Breeding system properties, including the number of breeders in a social group, their genetic relatedness, and skew in their parentage, determine group composition and the distribution of genetic variation within and between social units. This group genetic structure in turn influences the opportunities for conflict and cooperation to evolve within groups and for selection to occur among groups or clusters of groups. Thus, molecular studies of social groups provide the starting point for analyses of the selective forces involved in social evolution, as well as for analyses of other fundamental evolutionary problems related to sex allocation, reproductive skew, life history evolution, and the nature of selection in hierarchically structured populations. The framework presented here provides a standard system for interpreting and integrating genetic and natural history data from social organisms for application to a broad range of evolutionary questions. [source]


Organizational Slack and Corporate Greening: Broadening the Debate

BRITISH JOURNAL OF MANAGEMENT, Issue 4 2002
Frances E. Bowen
Organizational slack seems to have an ambiguous relationship with corporate greening. On the one hand, excess resources can be used to experiment with new environmental innovations, or potential green market segments. On the other, excess resources can be used to build corporate buffers against pressures for environmental improvement, such as large corporate environmental departments or environmental lobbying activity, and resist changes to the core of the organization. This paper begins to resolve these conflicting arguments by broadening the debate on organizational slack and corporate greening. It builds on recent empirical studies of slack and corporate greening, and recognizes the many potential roles that different types of slack may play in a dynamic decision,making context. Using a theoretical framework suggested by Bourgeois (1981), the paper systematizes and draws lessons from examples of the roles of slack encountered in a recent series of 35 interviews within UK public limited companies. It concludes that future treatments of slack and environmental management should incorporate a more holistic view of slack, which recognizes its dynamic, complex and often contradictory effects on decision,making in organizations. [source]