608 research outputs found
A Design and Analytic Strategy for Monitoring Disease Positivity and Case Characteristics in Accessible Closed Populations
We propose a monitoring strategy for efficient and robust estimation of
disease prevalence and case numbers within closed and enumerated populations
such as schools, workplaces, or retirement communities. The proposed design
relies largely on voluntary testing, notoriously biased (e.g., in the case of
COVID-19) due to non-representative sampling. The approach yields unbiased and
comparatively precise estimates with no assumptions about factors underlying
selection of individuals for voluntary testing, building on the strength of
what can be a small random sampling component. This component unlocks a
previously proposed "anchor stream" estimator, a well-calibrated alternative to
classical capture-recapture (CRC) estimators based on two data streams. We show
here that this estimator is equivalent to a direct standardization based on
"capture", i.e., selection (or not) by the voluntary testing program, made
possible by means of a key parameter identified by design. This equivalency
simultaneously allows for novel two-stream CRC-like estimation of general means
(e.g., of continuous variables such as antibody levels or biomarkers). For
inference, we propose adaptations of a Bayesian credible interval when
estimating case counts and bootstrapping when estimating means of continuous
variables. We use simulations to demonstrate significant precision benefits
relative to random sampling alone
Enhanced Inference for Finite Population Sampling-Based Prevalence Estimation with Misclassification Errors
Epidemiologic screening programs often make use of tests with small, but
non-zero probabilities of misdiagnosis. In this article, we assume the target
population is finite with a fixed number of true cases, and that we apply an
imperfect test with known sensitivity and specificity to a sample of
individuals from the population. In this setting, we propose an enhanced
inferential approach for use in conjunction with sampling-based bias-corrected
prevalence estimation. While ignoring the finite nature of the population can
yield markedly conservative estimates, direct application of a standard finite
population correction (FPC) conversely leads to underestimation of variance. We
uncover a way to leverage the typical FPC indirectly toward valid statistical
inference. In particular, we derive a readily estimable extra variance
component induced by misclassification in this specific but arguably common
diagnostic testing scenario. Our approach yields a standard error estimate that
properly captures the sampling variability of the usual bias-corrected maximum
likelihood estimator of disease prevalence. Finally, we develop an adapted
Bayesian credible interval for the true prevalence that offers improved
frequentist properties (i.e., coverage and width) relative to a Wald-type
confidence interval. We report the simulation results to demonstrate the
enhanced performance of the proposed inferential methods
Tailoring Capture-Recapture Methods to Estimate Registry-Based Case Counts Based on Error-Prone Diagnostic Signals
Surveillance research is of great importance for effective and efficient
epidemiological monitoring of case counts and disease prevalence. Taking
specific motivation from ongoing efforts to identify recurrent cases based on
the Georgia Cancer Registry, we extend recently proposed "anchor stream"
sampling design and estimation methodology. Our approach offers a more
efficient and defensible alternative to traditional capture-recapture (CRC)
methods by leveraging a relatively small random sample of participants whose
recurrence status is obtained through a principled application of medical
records abstraction. This sample is combined with one or more existing
signaling data streams, which may yield data based on arbitrarily
non-representative subsets of the full registry population. The key extension
developed here accounts for the common problem of false positive or negative
diagnostic signals from the existing data stream(s). In particular, we show
that the design only requires documentation of positive signals in these
non-anchor surveillance streams, and permits valid estimation of the true case
count based on an estimable positive predictive value (PPV) parameter. We
borrow ideas from the multiple imputation paradigm to provide accompanying
standard errors, and develop an adapted Bayesian credible interval approach
that yields favorable frequentist coverage properties. We demonstrate the
benefits of the proposed methods through simulation studies, and provide a data
example targeting estimation of the breast cancer recurrence case count among
Metro Atlanta area patients from the Georgia Cancer Registry-based Cancer
Recurrence Information and Surveillance Program (CRISP) database
The Ultraviolet Imaging Telescope: Instrument and Data Characteristics
The Ultraviolet Imaging Telescope (UIT) was flown as part of the Astro
observatory on the Space Shuttle Columbia in December 1990 and again on the
Space Shuttle Endeavor in March 1995. Ultraviolet (1200-3300 Angstroms) images
of a variety of astronomical objects, with a 40 arcmin field of view and a
resolution of about 3 arcsec, were recorded on photographic film. The data
recorded during the first flight are available to the astronomical community
through the National Space Science Data Center (NSSDC); the data recorded
during the second flight will soon be available as well. This paper discusses
in detail the design, operation, data reduction, and calibration of UIT,
providing the user of the data with information for understanding and using the
data. It also provides guidelines for analyzing other astronomical imagery made
with image intensifiers and photographic film.Comment: 44 pages, LaTeX, AAS preprint style and EPSF macros, accepted by PAS
An Ultraviolet and Near-Infrared View of NGC 4214: A Starbursting Core Embedded in a Low Surface Brightness Disk
During the Astro-2 Spacelab mission in 1995 March, the Ultraviolet Imaging Telescope (UIT) obtained far-UV (λ = 1500 A) imagery of the nearby Sm/Im galaxy NGC 4214. The UIT images have a spatial resolution of ~3'' and a limiting surface brightness, ÎŒ1500 > 25 mag arcsec-2, permitting detailed investigation of the intensity and spatial distribution of the young, high-mass stellar component. These data provide the first far-UV imagery covering the full spatial extent of NGC 4214. Comparison with a corresponding I-band image reveals the presence of a starbursting core embedded in an extensive low surface brightness disk. In the far-UV (FUV), NGC 4214 is resolved into several components: a luminous, central knot; an inner region (r 2.5 kpc) with ~15 resolved sources embedded in bright, diffuse emission; and a population of fainter knots extending to the edge of the optically defined disk (r â 5 kpc). The FUV light, which traces recent massive star formation, is observed to be more centrally concentrated than the I-band light, which traces the global stellar population. The FUV radial light profile is remarkably well represented by an R1/4 law, providing evidence that the centrally concentrated massive star formation in NGC 4214 is the result of an interaction, possibly a tidal encounter, with a dwarf companion(s). The brightest FUV source produces ~8% of the global FUV luminosity. This unresolved source, corresponding to the Wolf-Rayet knot described by Sargent & Filippenko, is located at the center of the FUV light distribution, giving NGC 4214 an active galactic nucleus-like morphology. Another strong source is present in the I band, located 19'' west, 10'' north of the central starburst knot, with no FUV counterpart. The I-band source may be the previously unrecognized nucleus of NGC 4214 or an evolved star cluster with an age greater than ~200 Myr. The global star formation rate derived from the total FUV flux is consistent with rates derived using data at other wavelengths and lends support to the scenario of roughly constant star formation during the last few hundred million years at a level significantly enhanced relative to the lifetime averaged star formation rate. The hybrid disk/starburst-irregular morphology evident in NGC 4214 emphasizes the danger of classifying galaxies based on their high surface brightness components at any particular wavelength
Periurban Trypanosoma cruziâinfected Triatoma infestans, Arequipa, Peru
Simple interventions may facilitate vector control and prevent periurban transmission of Chagas disease
Applications of a New Proposal for Solving the "Problem of Time" to Some Simple Quantum Cosmological Models
We apply a recent proposal for defining states and observables in quantum
gravity to simple models. First, we consider a Klein-Gordon particle in an ex-
ternal potential in Minkowski space and compare our proposal to the theory ob-
tained by deparametrizing with respect to a time slicing prior to quantiza-
tion. We show explicitly that the dynamics of the deparametrization approach
depends on the time slicing. Our proposal yields a dynamics independent of the
choice of time slicing at intermediate times but after the potential is turned
off, the dynamics does not return to the free particle dynamics. Next we apply
our proposal to the closed Robertson-Walker quantum cosmology with a massless
scalar field with the size of the universe as our time variable, so the only
dynamical variable is the scalar field. We show that the resulting theory has
the semi-classical behavior up to the classical turning point from expansion to
contraction, i.e., given a classical solution which expands for much longer
than the Planck time, there is a quantum state whose dynamical evolution
closely approximates this classical solution during the expansion. However,
when the "time" gets larger than the classical maximum, the scalar field be-
comes "frozen" at its value at the maximum expansion. We also obtain similar
results in the Taub model. In an Appendix we derive the form of the Wheeler-
DeWitt equation for the Bianchi models by performing a proper quantum reduc-
tion of the momentum constraints; this equation differs from the usual one ob-
tained by solving the momentum constraints classically, prior to quantization.Comment: 30 pages, LaTeX 3 figures (postscript file or hard copy) available
upon request, BUTP-94/1
Cardiovascular magnetic resonance of the charcoal heart
We report a case of malignant melanoma metastasis to the heart presenting as complete heart block. The highlight of the case is to demonstrate that silent cardiac metastasis is not uncommon and CMR has the potential to characterize these cardiac metastases and should be used routinely as a screening tool for those cancers with a high chance of cardiac involvement
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