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Articles 1 - 20 of 20
Full-Text Articles in Physical Sciences and Mathematics
Quantitative Evaluation Of Hiv Preventon Programs, Edward Kaplan, Ron Brookmeyer
Quantitative Evaluation Of Hiv Preventon Programs, Edward Kaplan, Ron Brookmeyer
Ron Brookmeyer
How successful are HIV prevention programs? Which HIV prevention programs are most cost effective? Which programs are worth expanding and which should be abandoned altogether? This book addresses the quantitative evaluation of HIV prevention programs, assessing for the first time several different quantitative methods of evaluation
Prevention Of Inhalational Anthrax In The U.S. Outbreak, Ron Brookmeyer, Natalie Blades
Prevention Of Inhalational Anthrax In The U.S. Outbreak, Ron Brookmeyer, Natalie Blades
Ron Brookmeyer
No abstract provided.
A Study Of Indoor Carbon Dioxide Levels And Sick Leave Among Office Workers, Theodore A. Myatt, John W. Staudenmayer, Kate Adams, Michael Walters, Stephen N. Rudnick, Donald K. Milton
A Study Of Indoor Carbon Dioxide Levels And Sick Leave Among Office Workers, Theodore A. Myatt, John W. Staudenmayer, Kate Adams, Michael Walters, Stephen N. Rudnick, Donald K. Milton
John W Staudenmayer
Background A previous observational study detected a strong positive relationship between sick leave absences and carbon dioxide (CO2) concentrations in office buildings in the Boston area. The authors speculated that the observed association was due to a causal effect associated with low dilution ventilation, perhaps increased airborne transmission of respiratory infections. This study was undertaken to explore this association. Methods We conducted an intervention study of indoor CO2 levels and sick leave among hourly office workers employed by a large corporation. Outdoor air supply rates were adjusted periodically to increase the range of CO2 concentrations. We recorded indoor CO2 concentrations …
Fast Fifth-Order Polynomial Transforms For Generating Univariate And Multivariate Nonnormal Distributions, Todd C. Headrick
Fast Fifth-Order Polynomial Transforms For Generating Univariate And Multivariate Nonnormal Distributions, Todd C. Headrick
Todd Christopher Headrick
A general procedure is derived for simulating univariate and multivariate nonnormal distributions using polynomial transformations of order five. The procedure allows for the additional control of the fifth and sixth moments. The ability to control higher moments increases the precision in the approximations of nonnormal distributions and lowers the skew and kurtosis boundary relative to the competing procedures considered. Tabled values of constants are provided for approximating various probability density functions. A numerical example is worked to demonstrate the multivariate procedure. The results of a Monte Carlo simulation are provided to demonstrate that the procedure generates specified population parameters and …
Expressing Logistic Regression Coefficients As Changes In Initial Probability Values: Useful Information For Practitioners, John Fraas, J Michael Drushal, Jef Graham
Expressing Logistic Regression Coefficients As Changes In Initial Probability Values: Useful Information For Practitioners, John Fraas, J Michael Drushal, Jef Graham
John W. Fraas
No abstract provided.
A Bayesian Analysis Involving Colonic Crypt Structure And Coordinated Response To Carcinogens Incorporating Missing Crypts, Jeffrey S. Morris, Naisyin Wang, Joanne R. Lupton, Robert S. Chapkin, Nancy D. Turner, Mee-Young Hong, Raymond J. Carroll
A Bayesian Analysis Involving Colonic Crypt Structure And Coordinated Response To Carcinogens Incorporating Missing Crypts, Jeffrey S. Morris, Naisyin Wang, Joanne R. Lupton, Robert S. Chapkin, Nancy D. Turner, Mee-Young Hong, Raymond J. Carroll
Jeffrey S. Morris
This paper is concerned with modeling the architecture of colonic crypts and the implications of this modeling for understanding possible coordinated response of carcinogen–induced DNA damage between various regions of the colon. The methods we develop to address these two issues are applied to a particular important example in colon carcinogenesis. We cast the problem as an unusual and not previously studied hierarchical mixed-effects model characterized by completely missing covariates in units at a structurally base level, except for some randomly selected units. Information concerning the missing covariates is available through certain known ordering constraints and surrogate measures. Our methods …
Robust Estimation Of Origin-Destination Matrices, Byron J. Gajewski, Laurence R Rilett, Michael P. Dixon, Clifford H. Spiegelman
Robust Estimation Of Origin-Destination Matrices, Byron J. Gajewski, Laurence R Rilett, Michael P. Dixon, Clifford H. Spiegelman
Byron J Gajewski
The demand for travel on a network is usually represented by an origin-destination (OD) trip table or matrix. OD trip tables are typically estimated with synthetic techniques that use observed data from the traffic system, such as link volume counts from intelligent transportation systems (ITS), as input. A potential problem with current estimation techniques is that many ITS volume counters have a relatively high error rate. The focus of this paper is on the development of estimators explicitly designed to be robust to outliers typically encountered in ITS. Equally important, standard errors are developed so that the parameter reliability can …
The Blups Are Not “Best” When It Comes To Bootstrapping, Jeffrey S. Morris
The Blups Are Not “Best” When It Comes To Bootstrapping, Jeffrey S. Morris
Jeffrey S. Morris
In the setting of mixed models, some researchers may construct a semiparametric bootstrap by sampling from the best linear unbiased predictor residuals. This paper demonstrates both mathematically and by simulation that such a bootstrap will consistently underestimate the variation in the data in finite samples.
Statistical Properties Of Composite Distortions In Hfc Systems And Their Effects On Digital Channels, Ron D. Katznelson
Statistical Properties Of Composite Distortions In Hfc Systems And Their Effects On Digital Channels, Ron D. Katznelson
Ron D. Katznelson
The statistical properties of Composite Triple Beat (CTB) and Composite Second Order (CSO) distortion terms associated with the analog channels carried on Hybrid Fiber Coax (HFC) are presented. Both simulation and measurement results show that such distortion components falling on individual channels have amplitude Probability Density Function that is nearly Rayleigh distributed (having a Standard Deviation of 5.7 dB). It is shown that both CTB and CSO components have peak envelope power fluctuations that exceed their average (measured) power levels by more than 15 dB. The temporal statistical properties of these distortion components demonstrate peak envelope power fluctuations with characteristic …
On The Existence Of Multiple Positive Solutions For A Semilinear Problem In Exterior Domains, Yinbin Deng, Yi Li
On The Existence Of Multiple Positive Solutions For A Semilinear Problem In Exterior Domains, Yinbin Deng, Yi Li
Yi Li
In this paper, we study the existence and nonexistence of multiple positive solutions for problem where Ω=N\ω is an exterior domain in N, ω⊂N is a bounded domain with smooth boundary, and N>2. μ⩾0, p>1 are some given constants. K(x) satisfies: K(x)∈Cαloc(Ω) and ∃C, ϵ, M>0 such that |K(x)|⩽C |x|l for any |x|⩾M, with l⩽ −2−ϵ. Some existence and …
The Aging And Dying Processes And The Health Of Older Adults, Paula Diehr
The Aging And Dying Processes And The Health Of Older Adults, Paula Diehr
Paula Diehr
It is difficult to distinguish changes in health due to aging from those related to dying, because the two processes are highly related. Some potentially treatable conditions may mistakenly be dismissed as due to old age. The goal of this article was to examine the relationships of aging and of dying to changes in 10 health-related variables: self-rated health, depression, ADLs, IADLs, minimental state examination, body mass index, blocks walked per week, bed days, hospitalization, and walking speed (all coded so that higher values were better). We used longitudinal data from the Cardiovascular Health Study to estimate the changes in …
Can Law And Economics Be Both Practical And Principled?, David A. Hoffman, Michael P. O'Shea
Can Law And Economics Be Both Practical And Principled?, David A. Hoffman, Michael P. O'Shea
David A Hoffman
This article describes important recent developments in normative law and economics, and the difficulties they create for the project of efficiency-based legal reform. After long proceeding without a well articulated moral justification for using economic decision procedures to choose legal rules, scholars have lately begun to devote serious attention to developing a philosophically attractive definition of well-being. At the same time, the empirical side of law and economics is also being enriched with an improved understanding of the complexities of individuals' decision-making behavior. That is where the problems begin. Scholars may have better, more plausible conceptions of well-being in hand, …
The Importance Of The Normality Assumption In Large Public Health Data Sets, Paula Diehr, Thomas Lumley
The Importance Of The Normality Assumption In Large Public Health Data Sets, Paula Diehr, Thomas Lumley
Paula Diehr
It is widely but incorrectly believed that the t-test and linear regression are valid only for Normally distributed outcomes. The t-test and linear regression compare the mean of an outcome variable for different subjects. While these are valid even in very small samples if the outcome variable is Normally distributed, their major usefulness comes from the fact that in large samples they are valid for any distribution. We demonstrate this validity by simulation in extremely non-Normal data. We discuss situations in which in other methods such as the Wilcoxon rank sum test and ordinal logistic regression (proportional odds model) have …
Weight-Modification Trials In Older Adults: What Should The Outcome Measure Be?, Paula Diehr
Weight-Modification Trials In Older Adults: What Should The Outcome Measure Be?, Paula Diehr
Paula Diehr
BACKGROUND: Overweight older adults are often counseled to lose weight, even though there is little evidence of excess mortality in that age group. Overweight and underweight may be more associated with health status than with mortality, but few clinical trials of any kind have been based on maximizing years of healthy life (YHL), as opposed to years of life (YOL). OBJECTIVE: This paper examines the relationship of body mass index (BMI) to both YHL and YOL. Results were used to determine whether clinical trials of weight-modification based on improving YHL would be more powerful than studies based on survival. DESIGN: …
Unemployment Scarring In High Unemployment Regions, Claudio Lupi, Patrizia Ordine
Unemployment Scarring In High Unemployment Regions, Claudio Lupi, Patrizia Ordine
Claudio Lupi
This paper investigates the effect of individual unemployment experiences on re-employment wages. The empirical analysis is carried out on a panel of Italian individuals. The main result is that while in the northern regions the effect is similar to the one estimated for the UK, in the southern area of the country the impact is not significant. We link this result to the particular socio-economic environment in which the unemployment spells are experienced. We argue that this might be due to the fact that in a high unemployment environment individual unemployment experiences are perceived as "normal" and do not necessarily …
Rockets And Feathers Revisited: An International Comparison On European Gasoline Markets, Marzio Galeotti, Alessandro Lanza, Matteo Manera
Rockets And Feathers Revisited: An International Comparison On European Gasoline Markets, Marzio Galeotti, Alessandro Lanza, Matteo Manera
Matteo Manera
This paper re-examines the issue of asymmetries in the transmission of shocks to crude oil prices onto the retail price of gasoline. Relative to the previous literature, the distinguishing features of the present paper are: i) use of updated and comparable data to carry out an international comparison of gasoline markets; ii) two-stage modeling of the transmission of oil price shocks to gasoline prices (first refinery stage and second distribution stage), in order to assess possible asymmetries at either one or both stages; iii) use of asymmetric error correction models to distinguish between asymmetries that arise from short-run deviations in …
On Thickness And Packing Density For Knots And Links, Robert Kusner
On Thickness And Packing Density For Knots And Links, Robert Kusner
Robert Kusner
We describe some problems, observations, and conjectures concerning density of the hexagonal packing of unit disks in R2.thickness and packing density of knots and links in S3 and R3. We prove the thickness of a nontrivial knot or link in S3 is no more than 4 , the thickness of a Hopf link. We also give arguments and evidence supporting the conjecture that the packing density of thick links in R3 or S3 is generally less than √12 , the density of the hexagonal packing of unit disks in R2.
Statistical Issues In The Clustering Of Gene Expression Data, Darlene R. Goldstein, Debashis Ghosh, Erin M. Conlon
Statistical Issues In The Clustering Of Gene Expression Data, Darlene R. Goldstein, Debashis Ghosh, Erin M. Conlon
Erin M. Conlon
This paper illustrates some of the problems which can occur in any data set when clustering samples of gene expression profiles. These include a possible high degree of dependence of results on choice of clustering algorithm, further dependence of results on the choices of genes and samples to be included in the clustering (for example, whether or not to include control samples), and difficulty in assessing the validity of the grouping. We also demonstrate the use of Cox regression as a tool to identify genes influencing survival.
Optimal Policies For Investment With Time-Varying Return Distributions, Douglas Steigerwald, Doncho Donchev, Svetlozar Rachev
Optimal Policies For Investment With Time-Varying Return Distributions, Douglas Steigerwald, Doncho Donchev, Svetlozar Rachev
Douglas G. Steigerwald
We develop a model in which investors must learn the distribution of asset returns over time. The process of learning is made more difficult by the fact that the distributions are not constant through time. We consider risk-neutral investors who have quadratic utility and are selecting between two risky assets. We determine the time at which it is optimal to update the distribution estimate and, hence, alter portfolio weights. Our results deliver an optimal policy for asset allocation, that is, the sequence of time intervals at which it is optimal to switch between assets, based on stochastic optimal control theory. …
Forecasting Volatility In European Stock Markets With Non-Linear Garch Models, Giancarlo Forte, Matteo Manera
Forecasting Volatility In European Stock Markets With Non-Linear Garch Models, Giancarlo Forte, Matteo Manera
Matteo Manera
This paper investigates the forecasting performance of three popular variants of the nonlinear GARCH models, namely VS-GARCH, GJR-GARCH and Q-GARCH, with the symmetric GARCH(1,1) model as a benchmark. The application involves ten European stock price indexes. Forecasts produced by each non-linear GARCH model and each index are evaluated using a common set of classical criteria, as well as forecast combination techniques with constant and non-constant weights. With respect to the standard GARCH specification, the non-linear models generally lead to better forecasts in terms of both smaller forecast errors and lower biases. In-sample forecast combination regressions are better than those from …