15 research outputs found
Bivariate least squares linear regression: towards a unified analytic formalism
Concerning bivariate least squares linear regression, the classical approach
pursued for functional models in earlier attempts is reviewed using a new
formalism in terms of deviation (matrix) traces. Within the framework of
classical error models, the dependent variable relates to the independent
variable according to the usual additive model. Linear models of regression
lines are considered in the general case of correlated errors in X and in Y for
heteroscedastic data. The special case of (C) generalized orthogonal regression
is considered in detail together with well known subcases. In the limit of
homoscedastic data, the results determined for functional models are compared
with their counterparts related to extreme structural models. While regression
line slope and intercept estimators for functional and structural models
necessarily coincide, the contrary holds for related variance estimators even
if the residuals obey a Gaussian distribution, with a single exception. An
example of astronomical application is considered, concerning the [O/H]-[Fe/H]
empirical relations deduced from five samples related to different stars and/or
different methods of oxygen abundance determination. For selected samples and
assigned methods, different regression models yield consistent results within
the errors for both heteroscedastic and homoscedastic data. Conversely, samples
related to different methods produce discrepant results, due to the presence of
(still undetected) systematic errors, which implies no definitive statement can
be made at present. A comparison is also made between different expressions of
regression line slope and intercept variance estimators, where fractional
discrepancies are found to be not exceeding a few percent, which grows up to
about 20% in presence of large dispersion data.Comment: 56 pages, 2 tables, and 2 figures. New Astronomy, accepte
Beyond chance? The persistence of performance in online poker
A major issue in the widespread controversy about the legality of poker and the appropriate taxation of winnings is whether poker should be considered a game of skill or a game of chance. To inform this debate we present an analysis into the role of skill in the performance of online poker players, using a large database with hundreds of millions of player-hand observations from real money ring games at three different stakes levels. We find that players whose earlier profitability was in the top (bottom) deciles perform better (worse) and are substantially more likely to end up in the top (bottom) performance deciles of the following time period. Regression analyses of performance on historical performance and other skill-related proxies provide further evidence for persistence and predictability. Simulations point out that skill dominates chance when performance is measured over 1,500 or more hands of play
Determination of the Deep Inelastic Contribution to the Generalised Gerasimov-Drell-Hearn Integral for the Proton and Neutron
The virtual photon absorption cross section differences [sigma_1/2-sigma_3/2]
for the proton and neutron have been determined from measurements of polarised
cross section asymmetries in deep inelastic scattering of 27.5 GeV
longitudinally polarised positrons from polarised 1H and 3He internal gas
targets. The data were collected in the region above the nucleon resonances in
the kinematic range nu < 23.5 GeV and 0.8 GeV**2 < Q**2 < 12 GeV**2. For the
proton the contribution to the generalised Gerasimov-Drell-Hearn integral was
found to be substantial and must be included for an accurate determination of
the full integral. Furthermore the data are consistent with a QCD
next-to-leading order fit based on previous deep inelastic scattering data.
Therefore higher twist effects do not appear significant.Comment: 6 pages, 3 figures, 1 table, revte
Observation of a Coherence Length Effect in Exclusive Rho^0 Electroproduction
Exclusive incoherent electroproduction of the rho^0(770) meson from 1H, 2H,
3He, and 14N targets has been studied by the HERMES experiment at squared
four-momentum transfer Q**2>0.4 GeV**2 and positron energy loss nu from 9 to 20
GeV. The ratio of the 14N to 1H cross sections per nucleon, known as the
nuclear transparency, was found to decrease with increasing coherence length of
quark-antiquark fluctuations of the virtual photon. The data provide clear
evidence of the interaction of the quark- antiquark fluctuations with the
nuclear medium.Comment: RevTeX, 5 pages, 3 figure
Application of a diagnosis-based clinical decision guide in patients with neck pain
<p>Abstract</p> <p>Background</p> <p>Neck pain (NP) is a common cause of disability. Accurate and efficacious methods of diagnosis and treatment have been elusive. A diagnosis-based clinical decision guide (DBCDG; previously referred to as a diagnosis-based clinical decision rule) has been proposed which attempts to provide the clinician with a systematic, evidence-based guide in applying the biopsychosocial model of care. The approach is based on three questions of diagnosis. The purpose of this study is to present the prevalence of findings using the DBCDG in consecutive patients with NP.</p> <p>Methods</p> <p>Demographic, diagnostic and baseline outcome measure data were gathered on a cohort of NP patients examined by one of three examiners trained in the application of the DBCDG.</p> <p>Results</p> <p>Data were gathered on 95 patients. Signs of visceral disease or potentially serious illness were found in 1%. Centralization signs were found in 27%, segmental pain provocation signs were found in 69% and radicular signs were found in 19%. Clinically relevant myofascial signs were found in 22%. Dynamic instability was found in 40%, oculomotor dysfunction in 11.6%, fear beliefs in 31.6%, central pain hypersensitivity in 4%, passive coping in 5% and depression in 2%.</p> <p>Conclusion</p> <p>The DBCDG can be applied in a busy private practice environment. Further studies are needed to investigate clinically relevant means to identify central pain hypersensitivity, oculomotor dysfunction, poor coping and depression, correlations and patterns among the diagnostic components of the DBCDG as well as inter-examiner reliability, validity and efficacy of treatment based on the DBCDG.</p