1,839 research outputs found
Overstating the evidence - double counting in meta-analysis and related problems
Background: The problem of missing studies in meta-analysis has received much attention. Less attention has been paid to the more serious problem of double counting of evidence.
Methods: Various problems in overstating the precision of results from meta-analyses are described and illustrated with examples, including papers from leading medical journals. These problems include, but are not limited to, simple double-counting of the same studies, double counting of some aspects of the studies, inappropriate imputation of results, and assigning spurious precision to individual studies.
Results: Some suggestions are made as to how the quality and reliability of meta-analysis can be improved. It is proposed that the key to quality in meta-analysis lies in the results being transparent and checkable.
Conclusions: Existing quality check lists for meta-analysis do little to encourage an appropriate attitude to combining evidence and to statistical analysis. Journals and other relevant organisations should encourage authors to make data available and make methods explicit. They should also act promptly to withdraw meta-analyses when mistakes are found
P-097. Luteinizing hormone urinary test is an efficient and cost-effective method to monitor ovulation for the transfer of cryopreserved embryos in natural cycles
Harold Jeffreys's Theory of Probability Revisited
Published exactly seventy years ago, Jeffreys's Theory of Probability (1939)
has had a unique impact on the Bayesian community and is now considered to be
one of the main classics in Bayesian Statistics as well as the initiator of the
objective Bayes school. In particular, its advances on the derivation of
noninformative priors as well as on the scaling of Bayes factors have had a
lasting impact on the field. However, the book reflects the characteristics of
the time, especially in terms of mathematical rigor. In this paper we point out
the fundamental aspects of this reference work, especially the thorough
coverage of testing problems and the construction of both estimation and
testing noninformative priors based on functional divergences. Our major aim
here is to help modern readers in navigating in this difficult text and in
concentrating on passages that are still relevant today.Comment: This paper commented in: [arXiv:1001.2967], [arXiv:1001.2968],
[arXiv:1001.2970], [arXiv:1001.2975], [arXiv:1001.2985], [arXiv:1001.3073].
Rejoinder in [arXiv:0909.1008]. Published in at
http://dx.doi.org/10.1214/09-STS284 the Statistical Science
(http://www.imstat.org/sts/) by the Institute of Mathematical Statistics
(http://www.imstat.org
O-105. Follow-up of 100 children, aged 1 and 2 years, born after intracytoplasmic sperm injection
The Principles at Work In High Performing Information Systems Organizations
Although there is a great deal of discussion about high performing information systems (I/S) organizations, little is known about the characteristics and practices they use. A field study was conducted to learn what principles are applied in organizations widely acknowledged to be high performers. The sample of companies for this field study was chosen by a core team of 15 consultants, practitioners, and academic researchers. On-site, structured interviews were conducted with 105 executives and managers in both the functional areas and the I/S groups of the firms. The findings show that a common set of principles are applied in high performing I/S groups. At the same time, there are distinct differences between these leading companies. The results provide useful insights for practice and for future research
The Woods-Saxon Potential in the Dirac Equation
The two-component approach to the one-dimensional Dirac equation is applied
to the Woods-Saxon potential. The scattering and bound state solutions are
derived and the conditions for a transmission resonance (when the transmission
coefficient is unity) and supercriticality (when the particle bound state is at
E=-m) are then derived. The square potential limit is discussed. The recent
result that a finite-range symmetric potential barrier will have a transmission
resonance of zero-momentum when the corresponding well supports a half-bound
state at E=-m is demonstrated.Comment: 8 pages, 4 figures. Submitted to JPhys
Do ultra-runners in a 24-h run really dehydrate?
Background: Loss of body mass during a 24-h run was considered to be a result of dehydration. Aims: We intended to quantify the decrease in body mass as a loss in fat mass or skeletal muscle mass and to quantify the change in hydration status. Methods: Body mass, fat mass, skeletal muscle mass, haematocrit, plasma sodium and urinary specific gravity were measured in 15 ultra-marathoners in a 24-h run. Results: Body mass decreased by 2.2kg (p=0.0009) and fat mass decreased by 0.5kg (p=0.0084). The decrease in body mass correlated to the decrease in fat mass (r=0.72, p=0.0024). Urinary specific gravity increased from 1.012 to 1.022g/mL (p=0.0005). Conclusions: The decrease in body mass and the increase in urinary specific gravity indicate dehydration. The decrease in body mass was correlated to the decrease in fat mass and therefore not only due to dehydratio
P-220. Significance of non-placental pregnancy-specific α1-glycoprotein in the serum of IVF cycles before and after embryo transfer
Transmission resonances and supercritical states in a one dimensional cusp potential
We solve the two-component Dirac equation in the presence of a spatially one
dimensional symmetric cusp potential. We compute the scattering and bound
states solutions and we derive the conditions for transmission resonances as
well as for supercriticality.Comment: 10 pages. Revtex 4. To appear in Phys Rev.
O-006. Computerized fast-motion video capture of mouse embryo development and hatching: a comparative analysis between normal and assisted hatching
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