3,984 research outputs found
Why bayesian “evidence for H1” in one condition and bayesian “evidence for H0” in another condition does not mean good-enough bayesian evidence for a difference between the conditions
Psychologists are often interested in whether an independent variable has a different effect in condition A than in condition B. To test such a question, one needs to directly compare the effect of that variable in the two conditions (i.e., test the interaction). Yet many researchers tend to stop when they find a significant test in one condition and a nonsignificant test in the other condition, deeming this as sufficient evidence for a difference between the two conditions. In this Tutorial, we aim to raise awareness of this inferential mistake when Bayes factors are used with conventional cutoffs to draw conclusions. For instance, some researchers might falsely conclude that there must be good-enough evidence for the interaction if they find good-enough Bayesian evidence for the alternative hypothesis, H1, in condition A and good-enough Bayesian evidence for the null hypothesis, H0, in condition B. The case study we introduce highlights that ignoring the test of the interaction can lead to unjustified conclusions and demonstrates that the principle that any assertion about the existence of an interaction necessitates the direct comparison of the conditions is as true for Bayesian as it is for frequentist statistics. We provide an R script of the analyses of the case study and a Shiny app that can be used with a 2 × 2 design to develop intuitions on this issue, and we introduce a rule of thumb with which one can estimate the sample size one might need to have a well-powered design
Laser Doppler technology applied to atmospheric environmental operating problems
Carbon dioxide laser Doppler ground wind data were very favorably compared with data from standard anemometers. As a result of these measurements, two breadboard systems were developed for taking research data: a continuous wave velocimeter and a pulsed Doppler system. The scanning continuous wave laser Doppler velocimeter developed for detecting, tracking and measuring aircraft wake vortices was successfully tested at an airport where it located vortices to an accuracy of 3 meters at a range of 150 meters. The airborne pulsed laser Doppler system was developed to detect and measure clear air turbulence (CAT). This system was tested aboard an aircraft, but jet stream CAT was not encountered. However, low altitude turbulence in cumulus clouds near a mountain range was detected by the system and encountered by the aircraft at the predicted time
An investigation into the effect of varying plyometric volume on reactive strength and leg stiffness in collegiate rugby players
The purpose of this study was to identify the role that low and high volume plyometric
loads have on the effectiveness of developing stretch shortening cycle capability in
collegiate rugby players. The experiment was carried out utilising a between- group,
repeated measures design. Thirty six participants (Age 20.3 ±1.6 yrs, mass 91.63
±10.36kg, height 182.03 ±5.24cm) were randomly assigned to one of three groups, a
control group (CG), a low volume plyometric group (LPG) and a high volume plyometric
group (HPG). Data were collected from a force plate, and measures of reactive
strength index (RSI) and leg stiffness were calculated from jump height, contact time
and flight time data. Drop Jumps were used to gather data to measure RSI and double
leg hops were used to gather leg stiffness data. The analysis demonstrated an overall
significance in the interaction effect between group* time (F =4.01, p <0.05) for RSI.
Bonferroni post hoc analysis indicated that both the LPG training group (p = 0.002) and
HPG training group (p = 0.009) demonstrated a significance from the control group. No
significant interaction effect between time*group or main effect were observed for leg
stiffness (F = 1.39, p = .25). The current study has demonstrated that it is possible to
improve reactive strength capabilities to a significant level via the use of a low volume
plyometric programme. The low volume programme elicited the same performance
improvement in RSI values as a high volume programme whilst undertaking only a
quarter of the volume. This suggests that strength and conditioning coaches may be
able to benefit from the ability to develop more time efficient and effective plyometric
programmes
Bayesian Analysis of Inflation II: Model Selection and Constraints on Reheating
We discuss the model selection problem for inflationary cosmology. We couple
ModeCode, a publicly-available numerical solver for the primordial perturbation
spectra, to the nested sampler MultiNest, in order to efficiently compute
Bayesian evidence. Particular attention is paid to the specification of
physically realistic priors, including the parametrization of the
post-inflationary expansion and associated thermalization scale. It is
confirmed that while present-day data tightly constrains the properties of the
power spectrum, it cannot usefully distinguish between the members of a large
class of simple inflationary models. We also compute evidence using a simulated
Planck likelihood, showing that while Planck will have more power than WMAP to
discriminate between inflationary models, it will not definitively address the
inflationary model selection problem on its own. However, Planck will place
very tight constraints on any model with more than one observationally-distinct
inflationary regime -- e.g. the large- and small-field limits of the hilltop
inflation model -- and put useful limits on different reheating scenarios for a
given model.Comment: ModeCode package available from
http://zuserver2.star.ucl.ac.uk/~hiranya/ModeCode/ModeCode (requires CosmoMC
and MultiNest); to be published in PRD. Typos fixe
Constructing smooth potentials of mean force, radial, distribution functions and probability densities from sampled data
In this paper a method of obtaining smooth analytical estimates of
probability densities, radial distribution functions and potentials of mean
force from sampled data in a statistically controlled fashion is presented. The
approach is general and can be applied to any density of a single random
variable. The method outlined here avoids the use of histograms, which require
the specification of a physical parameter (bin size) and tend to give noisy
results. The technique is an extension of the Berg-Harris method [B.A. Berg and
R.C. Harris, Comp. Phys. Comm. 179, 443 (2008)], which is typically inaccurate
for radial distribution functions and potentials of mean force due to a
non-uniform Jacobian factor. In addition, the standard method often requires a
large number of Fourier modes to represent radial distribution functions, which
tends to lead to oscillatory fits. It is shown that the issues of poor sampling
due to a Jacobian factor can be resolved using a biased resampling scheme,
while the requirement of a large number of Fourier modes is mitigated through
an automated piecewise construction approach. The method is demonstrated by
analyzing the radial distribution functions in an energy-discretized water
model. In addition, the fitting procedure is illustrated on three more
applications for which the original Berg-Harris method is not suitable, namely,
a random variable with a discontinuous probability density, a density with long
tails, and the distribution of the first arrival times of a diffusing particle
to a sphere, which has both long tails and short-time structure. In all cases,
the resampled, piecewise analytical fit outperforms the histogram and the
original Berg-Harris method.Comment: 14 pages, 15 figures. To appear in J. Chem. Phy
Laser Doppler dust devil measurements
A scanning laser doppler velocimeter (SLDV) system was used to detect, track, and measure the velocity flow field of naturally occurring tornado-like flows (dust devils) in the atmosphere. A general description of the dust devil phenomenon is given along with a description of the test program, measurement system, and data processing techniques used to collect information on the dust devil flow field. The general meteorological conditions occurring during the test program are also described, and the information collected on two selected dust devils are discussed in detail to show the type of information which can be obtained with a SLDV system. The results from these measurements agree well with those of other investigators and illustrate the potential for the SLDV in future endeavors
Neuroendocrinology and resistance training in adult males
An understanding of the neuroendocrine system will assist the Strength and Conditioning coach in the design of progressive strength training programmes by allowing them to manipulate acute training variables according to hormone release profiles. For muscle hypertrophy, training programmes should utilise 3 sets of 10 repetitions at 10RM loads, with short rest periods of no longer than 1 minute. This will ensure the accumulation and maintenance of lactate and hydrogen ions, to which anabolic hormone release is correlated. For strength adaptations without
concomitant muscle hypertrophy, the training load and the length of rest periods should be increased, (>85% 1RM and >2mins respectively), and body parts should be rotated (e.g. upper body to lower body or agonist to antagonist). Finally, catabolic hormones and neurohormones significantly affect training adaptations. Therefore the strength and conditioning coach should be cognisant of the specific exercise programming and psychological interventions that manipulate their release
Testing and selection of cosmological models with corrections
In the paper we check whether the contribution of type in the
Friedmann equation can be tested. We consider some astronomical tests to
constrain the density parameters in such models. We describe different
interpretations of such an additional term: geometric effects of Loop Quantum
Cosmology, effects of braneworld cosmological models, non-standard cosmological
models in metric-affine gravity, and models with spinning fluid. Kinematical
(or geometrical) tests based on null geodesics are insufficient to separate
individual matter components when they behave like perfect fluid and scale in
the same way. Still, it is possible to measure their overall effect. We use
recent measurements of the coordinate distances from the Fanaroff-Riley type
IIb (FRIIb) radio galaxy (RG) data, supernovae type Ia (SNIa) data, baryon
oscillation peak and cosmic microwave background radiation (CMBR) observations
to obtain stronger bounds for the contribution of the type considered. We
demonstrate that, while corrections are very small, they can be tested
by astronomical observations -- at least in principle. Bayesian criteria of
model selection (the Bayesian factor, AIC, and BIC) are used to check if
additional parameters are detectable in the present epoch. As it turns out, the
CDM model is favoured over the bouncing model driven by loop quantum
effects. Or, in other words, the bounds obtained from cosmography are very
weak, and from the point of view of the present data this model is
indistinguishable from the CDM one.Comment: 19 pages, 1 figure. Version 2 generally revised and accepted for
publicatio
Determining the Neutrino Mass Hierarchy with Cosmology
The combination of current large scale structure and cosmic microwave
background (CMB) anisotropies data can place strong constraints on the sum of
the neutrino masses. Here we show that future cosmic shear experiments, in
combination with CMB constraints, can provide the statistical accuracy required
to answer questions about differences in the mass of individual neutrino
species. Allowing for the possibility that masses are non-degenerate we combine
Fisher matrix forecasts for a weak lensing survey like Euclid with those for
the forthcoming Planck experiment. Under the assumption that neutrino mass
splitting is described by a normal hierarchy we find that the combination
Planck and Euclid will possibly reach enough sensitivity to put a constraint on
the mass of a single species. Using a Bayesian evidence calculation we find
that such future experiments could provide strong evidence for either a normal
or an inverted neutrino hierachy. Finally we show that if a particular neutrino
hierachy is assumed then this could bias cosmological parameter constraints,
for example the dark energy equation of state parameter, by > 1\sigma, and the
sum of masses by 2.3\sigma.Comment: 9 pages, 6 figures, 3 table
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