8,517 research outputs found
Testing equality of variances in the analysis of repeated measurements
The problem of comparing the precisions of two instruments using repeated measurements can be cast as an extension of the Pitman-Morgan problem of testing equality of variances of a bivariate normal distribution. Hawkins (1981) decomposes the hypothesis of equal variances in this model into two subhypotheses for which simple tests exist. For the overall hypothesis he proposes to combine the tests of the subhypotheses using Fisher's method and empirically compares the component tests and their combination with the likelihood ratio test. In this paper an attempt is made to resolve some discrepancies and puzzling conclusions in Hawkins's study and to propose simple modifications.\ud
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The new tests are compared to the tests discussed by Hawkins and to each other both in terms of the finite sample power (estimated by Monte Carlo simulation) and theoretically in terms of asymptotic relative efficiencies
With a little help from my friends: Developing an assisted automated peritoneal dialysis program in Western Australia
Background: Nurse-assisted automated peritoneal dialysis (AAPD) offers a model of care that has been successfully used in frail dialysis populations internationally. AAPD offers cost savings over hospitalisation on peritoneal dialysis (PD) or in-centre haemodialysis (HD). Method: A pilot AAPD model of care was developed in Western Australia (WA). Patient evaluation was measured utilising a perceptions of dialysis survey, clinical events, hospitalisation and peritonitis rates, Charlson Comorbidity Index (CCI), KDQoL-SF 36 and a survey. Staff opinions and perceived competency were measured by an online survey. Economic analysis was undertaken. Results: A successful collaborative model was developed. 40 staff were trained and competency significantly improved during program delivery (p < 0.0001). 15 patients with an average CCI score of 8.7 used the service for 18 periods of care over 18 months (mean 33 days SD 47). Two non-renal cause deaths and two episodes of peritonitis occurred. Patient opinions were extremely positive. Cost savings were estimated at $620,000. Conclusion: In WA, an AAPD pilot program has been successfully developed and delivered. A sustainable model has overcome initial hurdles. Staff have gained new skills and delivered effective care, demonstrated by high patient acceptance. The program was cost-effective compared to staying in hospital or transferring to HD
A Fast Algorithm for Robust Regression with Penalised Trimmed Squares
The presence of groups containing high leverage outliers makes linear
regression a difficult problem due to the masking effect. The available high
breakdown estimators based on Least Trimmed Squares often do not succeed in
detecting masked high leverage outliers in finite samples.
An alternative to the LTS estimator, called Penalised Trimmed Squares (PTS)
estimator, was introduced by the authors in \cite{ZiouAv:05,ZiAvPi:07} and it
appears to be less sensitive to the masking problem. This estimator is defined
by a Quadratic Mixed Integer Programming (QMIP) problem, where in the objective
function a penalty cost for each observation is included which serves as an
upper bound on the residual error for any feasible regression line. Since the
PTS does not require presetting the number of outliers to delete from the data
set, it has better efficiency with respect to other estimators. However, due to
the high computational complexity of the resulting QMIP problem, exact
solutions for moderately large regression problems is infeasible.
In this paper we further establish the theoretical properties of the PTS
estimator, such as high breakdown and efficiency, and propose an approximate
algorithm called Fast-PTS to compute the PTS estimator for large data sets
efficiently. Extensive computational experiments on sets of benchmark instances
with varying degrees of outlier contamination, indicate that the proposed
algorithm performs well in identifying groups of high leverage outliers in
reasonable computational time.Comment: 27 page
Randomised, controlled trial of alternating pressure mattresses compared with alternating pressure overlays for the prevention of pressure ulcers : PRESSURE (pressure relieving support surfaces) trial
Objective To compare whether differences exist between alternating pressure overlays and alternating pressure mattresses in the development of new pressure ulcers, healing of existing pressure ulcers, and patient acceptability. Design Pragmatic, open, multicentre, randomised controlled trial. Setting 11 hospitals in six NHS trusts. Participants 1972 people admitted to hospital as acute or elective patients. Interventions Participants were randomised to an alternating pressure mattress (n = 982) of- an alternating pressure overlay (n = 990). Main outcome measures The proportion of participants developing a new pressure ulcer of grade 2 or worse; time to development of new pressure ulcers; proportions of participants developing a new ulcer within 30 days; healing of existing pressure ulcers; and patient acceptability Results Intention to treat analysis found no difference in the proportions of participants developing a new pressure ulcer of grade 2 or worse (10.7% overlay patients, 10.3% mattress patients; difference 0.4%, 95% confidence interval - 23% to 3.1%, P = 0.75). More overlay patients requested change owing to dissatisfaction (23.3%) than mattress patients (18.9%, P = 0.02). Conclusion No difference was found between alternating pressure mattresses and alternating pressure overlays in the proportion of people who develop a pressure ulcer
The X-ray Properties of z>4 Quasars
We report on a search for X-ray emission from quasars with redshifts greater
than four using the ROSAT public database. Our search has doubled the number of
z>4 quasars detected in X-rays from 6 to 12. Most of those known prior to this
work were radio-loud and X-ray selected sources; our study increases the number
of X-ray detected, optically selected z>4 quasars from one to seven. We present
their basic X-ray properties and compare these to those of lower redshift
quasars. We do not find any evidence for strong broad-band spectral differences
between optically selected z>4 quasars and those at lower redshifts.Comment: 7 pages, 4 figures included, LaTeX emulateapj.sty, accepted for
publication in the Astronomical Journa
Ranking ligand affinity for the DNA minor groove by experiment and simulation
The structural and thermodynamic basis for the strength and selectivity of the interactions of minor-groove binders (MGBs) with DNA is not fully understood. In 2003 we reported the first example of a thiazole containing MGB that bound in a phase shifted pattern that spanned 6 base-pairs rather than the usual 4 (for tricyclic distamycin-like compounds). Since then, using DNA footprinting, nuclear magnetic resonance spectroscopy, isothermal titration calorimetry and molecular dynamics, we have established that the flanking bases around the central 4 being read by the ligand have subtle effects on recognition. We have investigated the effect of these flanking sequences on binding and the reasons for the differences and established a computational method to rank ligand affinity against varying DNA sequences
A Study of CO Emission in High Redshift QSOs Using the Owens Valley Millimeter Array
Searches for CO emission in high-redshift objects have traditionally suffered
from the accuracy of optically-derived redshifts due to lack of bandwidth in
correlators at radio observatories. This problem has motivated the creation of
the new COBRA continuum correlator, with 4 GHz available bandwidth, at the
Owens Valley Radio Observatory Millimeter Array. Presented here are the first
scientific results from COBRA. We report detections of redshifted CO(J=3-2)
emission in the QSOs SMM J04135+10277 and VCV J140955.5+562827, as well as a
probable detection in RX J0911.4+0551. At redshifts of z=2.846, z=2.585, and
z=2.796, we find integrated CO flux densities of 5.4 Jy km/s, 2.4 Jy km/s, and
2.9 Jy km/s for SMM J04135+10277, VCV J140955.5+562827, and RX J0911.4+0551,
respectively, over linewidths of Delta(V_{FWHM}) ~ 350 km/s. These
measurements, when corrected for gravitational lensing, correspond to molecular
gas masses of order M(H_2) ~ 10^{9.6-11.1} solar masses, and are consistent
with previous CO observations of high-redshift QSOs. We also report 3-sigma
upper limits on CO(3-2) emission in the QSO LBQS 0018-0220 of 1.3 Jy km/s. We
do not detect significant 3mm continuum emission from any of the QSOs, with the
exception of a tentative (3-sigma) detection in RX J0911.4+0551 of S_{3mm}=0.92
mJy/beam.Comment: 18 pages, 5 figures, 2 tables, accepted to ApJ. Changes made for
version 2: citations added, 2 objects added to Table 2 and Figure
Have you a little fairy in your home?
Gift of Dr. Mary Jane Esplen.Piano vocal [instrumentation]Fancy the dusk of the [first line]Have you a little fairy, in your home, sweet home [first line of refrain]F [key]Tempo di valse [tempo]Popular song [form/genre]Elves in forest ; photograph of girl [illustration]J.H. Thomson [graphic artist]Publisher's advertisement on inside front and back cover [note]Title by permission of the N. K. Fairbank Co. [note
Have you a little fairy in your home?
Gift of Dr. Mary Jane Esplen.Piano vocal [instrumentation]Fancy the dusk of the [first line]Have you a little fairy, in your home, sweet home [first line of refrain]F [key]Tempo di valse [tempo]Popular song [form/genre]Elves in forest ; photograph of girl [illustration]J.H. Thomson [graphic artist]Publisher's advertisement on inside front and back cover [note]Title by permission of the N. K. Fairbank Co. [note
The Galactic Distribution of Phosphorus: A Survey of 163 Disk and Halo Stars
Phosphorus (P) is a critical element for life on Earth yet the cosmic
production sites of P are relatively uncertain. To understand how P has evolved
in the solar neighborhood, we measured abundances for 163 FGK stars over a
range of -1.09 [Fe/H] 0.47 using observations from the Habitable-zone
Planet Finder (HPF) instrument on the Hobby-Eberly Telescope (HET). Atmospheric
parameters were calculated by fitting a combination of astrometry, photometry,
and Fe I line equivalent widths. Phosphorus abundances were measured by
matching synthetic spectra to a P I feature at 10529.52 angstroms. Our [P/Fe]
ratios show that chemical evolution models generally under-predict P over the
observed metallicity range. Additionally, we find that the [P/Fe] differs by
0.1 dex between thin disk and thick disk stars that were identified with
kinematics. The P abundances were compared with -elements, iron-peak,
odd-Z, and s-process elements and we found that P in the disk most strongly
resembles the evolution of the -elements. We also find molar P/C and
N/C ratios for our sample match the scatter seen from other abundance studies.
Finally, we measure a [P/Fe] = 0.09 0.1 ratio in one low- halo
star and probable Gaia-Sausage-Enceladus (GSE) member, an abundance ratio
0.3 - 0.5 dex lower than the other Milky Way disk and halo stars at
similar metallicities. Overall, we find that P is likely most significantly
produced by massive stars in core collapse supernovae (CCSNe) based on the
largest P abundance survey to-date.Comment: 19 pages, 10 figures, accepted for publication in The Astronomical
Journa
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