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## Publications

Publications (105)

Background:
Care at verified trauma centers has improved survival and functional outcomes, yet determining the appropriate location of potential trauma centers is often driven by factors other than optimizing system-level patient care. Given the importance of transport time in trauma, we analyzed trauma transport patterns in a rural state lacking...

Background:
Agreement regarding indications for vena cava filter (VCF) utilization in trauma patients has been in flux since the filter's introduction. As VCF technology and practice guidelines have evolved, the use of VCF in trauma patients has changed. This study examines variation in VCF placement among trauma centers.
Materials and methods:...

Background:
Outcome prediction models allow risk adjustment required for trauma research and the evaluation of outcomes. The advent of ICD-10-CM has rendered risk adjustment based on ICD-9-CM codes moot, but as yet no risk adjustment model based on ICD-10-CM codes has been described.
Methods:
The National Trauma Data Bank provided data from 773,...

Firearm violence in the United States knows no age limit. This study compares the survival of children younger than five years to children and adolescents of age 5-19 years who presented to an ED for gunshot wounds (GSWs) in the United States to test the hypothesis of higher GSW mortality in very young children. A study of GSW patients aged 19 year...

Introduction:
Readmission following hospital discharge is both common and costly. The Hospital Readmission Reduction Program (HRRP) financially penalizes hospitals for readmission following admission for some conditions, but this approach may not be appropriate for all conditions. We wished to determine if hospitals differed in their adjusted read...

Background:
The Trauma Audit and Research Network (TARN) in the UK publicly reports hospital performance in the management of trauma. The TARN risk adjustment model uses a fractional polynomial transformation of the Injury Severity Score (ISS) as the measure of anatomical injury severity. The Trauma Mortality Prediction Model (TMPM) is an alternat...

Introduction:
The United States (US) leads all high income countries in gunshot wound (GSW) deaths. However, as a result of two decades of reduced federal support, study of GSW has been largely neglected. In this paper we describe the current state of GSW hospitalizations in the US using population-based data.
Patients and methods:
We conducted...

Massachusetts introduced health care reform (HCR) in 2006, expecting to expand health insurance coverage and improve outcomes. Because traumatic injury is a common acute condition with important health, disability, and economic consequences, examination of the effect of HCR on patients hospitalized following injury may help inform the national HCR...

Previous studies have reported that black race and lack of health insurance coverage are associated with increased mortality following traumatic injury. However, the association of race and insurance status with trauma outcomes has not been examined using contemporary, national, population-based data.
We used data from the National Inpatient Sample...

This article deals with the use of logistic regression to model data, where the response variable is binary and there are potentially numerous explanatory or predictor variables. Methods of estimating the coefficients in the model and procedures for hypothesis testing are considered. The correspondence of the coefficients of the logistic regression...

This article deals with the use of logistic regression to model data, where the response variable is binary and there are potentially numerous explanatory or predictor variables. Methods of estimating the coefficients in the model and procedures for hypothesis testing are considered. The correspondence of the coefficients of the logistic regression...

Performance benchmarking requires accurate measurement of injury severity. Despite its shortcomings, the Injury Severity Score (ISS) remains the industry standard 40 years after its creation. A new severity measure, the Trauma Mortality Prediction Model (TMPM), uses either the Abbreviated Injury Scale (AIS) or DRG International Classification of Di...

Complications are common in the care of trauma patients and contribute to morbidity, mortality, and cost. However, no comprehensive list of surgical complications is widely accepted.
To create an empirical list of complications based on the International Classification of Diseases, Ninth Revision (ICD-9) lexicon and estimate the contribution of the...

Context: Complications are common in the care of trauma patients and contribute to morbidity, mortality, and cost. However, no comprehensive list of surgical complications is widely accepted. Objectives: To create an empirical list of complications based on the International Classification of Diseases, Ninth Revision (ICD-9) lexicon and estimate th...

Introduction The Stratified Proportional Hazards Model Time-Varying Covariates Truncated, Left Censored and Interval Censored Data

Introduction Nominal Scale Covariate Continuous Scale Covariate Multiple-Covariate Models Interpreting and Using the Estimated Covariate-Adjusted Survival Function

Introduction Recurrent Event Models Frailty Models Nested Case-Control Studies Additive Models Competing Risk Models Sample Size and Power Missing Data

Introduction Estimating the Survival Function Using the Estimated Survival Function Comparison of Survival Functions Other Functions of Survival Time and Their Estimators

Introduction Purposeful Selection of Covariates Stepwise, Best-Subsets and Multivariable Fractional Polynomial Methods of Selecting Covariates Numerical Problems

Introduction Residuals Assessing the Proportional Hazards Assumption Identification of Influential and Poorly Fit Subjects Assessing Overall Goodness-of-Fit Interpreting and Presenting Results From the Final Model

Severity-adjusted mortality is an unequivocal measure of burn care success. Hospitals can be compared on this metric using administrative data because information required for calculating statistically adjusted risk of mortality is routinely collected on hospital admission.
The New York State Department of Health provided information on all 13,113...

: Generations of clinicians have used the Baux score, defined as the sum of age in years and percent body burn, to predict percent mortality after trauma, but advances in burn care have rendered the predictions of this score too pessimistic. Additionally, this score does not include the effects of inhalation injury.
: We revised the Baux score to i...

Logistic regression models are frequently used in epidemiological studies for estimating associations that demographic, behavioral, and risk factor variables have on a dichotomous outcome, such as disease being present versus absent. After the coefficients in a logistic regression model have been estimated, goodness-of-fit of the resulting model sh...

Little is known about the relationship of demographic, health, and psychosocial factors with health services utilization over time among low-income female heads of household. In a case-control study conducted between 1991 and 1997, 273 homeless and low-income housed mothers living in Worcester, Massachusetts were interviewed at baseline and at a tw...

This section describes the conditional logistic regression model. This model is appropriate when one wishes to model a binary outcome variable with matched or highly stratified data and when one is not interested in matched sets or stratum effects. The resulting fitted model may be used to estimate odds ratios in the same manner as is done with the...

This article deals with the use of logistic regression to model data, where the response variable is binary and there are potentially numerous explanatory or predictor variables. Methods of estimating the coefficients in the model and procedures for hypothesis testing are considered. The correspondence of the coefficients of the logistic regression...

IntroductionSummary Measures of Goodness-of-FitLogistic Regression DiagnosticsAssessment of Fit via External ValidationInterpretation and Presentation of the Results from a Fitted Logistic Regression ModelExercises

Grønnesby and Borgan (1996, Lifetime Data Analysis 2, 315-328) propose an omnibus goodness-of-fit test for the Cox proportional hazards model. The test is based on grouping the subjects by their estimated risk score and comparing the number of observed and a model based estimated number of expected events within each group. We show, using extensive...

While various goodness-of-fit tests have been developed to test the assumptions of the Cox proportional hazards model, this paper specifically examines the test proposed by Moreau, O'Quigley and Mesbah. We demonstrate that this test is algebraically identical to a test derived by adding group indicator variables to the model and testing the hypothe...

While various goodness-of-fit tests have been developed to test the assumptions of the Cox proportional hazards model, only a few are readily available in existing statistical software packages. We discuss previously proposed goodness-of-fit tests for the Cox model, which are of the Hosmer-Lemeshow type. We present results that show that the tests...

THE MOST PRACTICAL, UP-TO-DATE GUIDE TO MODELLING AND ANALYZING TIME-TO-EVENT DATANOW IN A VALUABLE NEW EDITION Since publication of the first edition nearly a decade ago, analyses using time-to-event methods have increase considerably in all areas of scientific inquiry mainly as a result of model-building methods available in modern statistical so...

Gronnesby and Borgan (1996) propose an overall goodness-of-fit test for the Cox proportional hazards model. The basis of their test is a grouping of subjects by their estimated risk score. We show that the Gronnesby and Borgan test is algebraically identical to one obtained from adding group indicator variables to the model and testing the hypothes...

This research was conducted to examine the effect of model choice on the epidemiologic interpretation of occupational cohort data. Three multiplicative models commonly employed in the analysis of occupational cohort studies--proportional hazards. Poisson, and logistic regression--were used to analyze data from an historical cohort study of workers...

Recent work has shown that there may be disadvantages in the use of the chi-square-like goodness-of-fit tests for the logistic regression model proposed by Hosmer and Lemeshow that use fixed groups of the estimated probabilities. A particular concern with these grouping strategies based on estimated probabilities, fitted values, is that groups may...

Recent work has shown that there may be disadvantages in the use of the chi-square-like goodness-of-fit tests for the logistic regression model proposed by Hosmer and Lemeshow that use fixed groups of the estimated probabilities. A particular concern with these grouping strategies based on estimated probabilities, fitted values, is that groups may...

Recent work has shown that there may be disadvantages in the use of the chi-square-like goodness-of-fit tests for the logistic regression model proposed by Hosmer and Lemeshow that use fixed groups of the estimated probabilities. A particular concern with these grouping strategies based on estimated probabilities, fitted values, is that groups may...

We evaluate performance of Mallows' Cp in best subsets selection for logistic and Poisson regression models using computer simulations. Comparison of success rate in recognizing correct and incorrect models is made with the likelihood ratio (LR) statistic and with the score statistic (S). We find that performance of Cp is compatible with that of LR...

To analyze the effects of patient mix diversity on performance of an intensive care unit (ICU) severity-of-illness model.
Multiple patient populations were created using computer simulations. A customized version of the Mortality Probability Model (MPM) II admission model was used to ascertain probabilities of hospital mortality. Performance of the...

Interaction, defined as departure of disease rates from an additive model, can be measured by the relative excess risk due to interaction, or the attributable proportion due to interaction. Point estimates can be obtained using multiple logistic regression. Using simulated case-control data, we compare several confidence interval estimation techniq...

To examine the impact of hospital mortality and intensive care unit (ICU) size on the performance of the Mortality Probability Model II system for use in quality assessment, and to examine the ability of model customization to produce accurate estimates of hospital mortality to characterize patients by severity of illness for clinical trials.
Prosp...

Background:
The impact of clinical trials on medical practice remains controversial, in part because of weak study designs and nonrepresentative study samples.Objective:
To assess changes in trends in medication use in the setting of acute myocardial infarction (AMI) before and after publication of two large clinical trials: the Second Internatio...

This paper considers an index of hospital quality performance defined as the ratio of the observed number deaths to the number predicted by a fitted logistic regression model. We study tests and confidence intervals under two different scenarios depending on the availability of an estimate of the covariance matrix of the coefficients from the fitte...

In the recent past, five methods for reducing computational intensity in best subset selection for Generalized Linear Models (GLM) have been proposed. We review these methods and explicitly show their mutual equivalence. Further, we show how the existing linear regression software can be used for such efficient best subset selection. Using the summ...

This survey was conducted to determine the frequency with which different data analysis techniques are being used in occupational cohort studies. Of particular interest was the relative use of external and internal comparison groups, and the choice of multivariable model.
Occupational cohort studies published in 1990-91 were located with Medline an...

Knowledge of BP variability is important for BP screening and for the design of studies with BP as an outcome. We calculated estimates of the between-visit and within-visit variances from data obtained using an automated BP.device (Dinamap) in 776 students, aged 13-17 years, in the Exeter-Andover Project. Each subject had his or her BP measured thr...

Part 1 Statistical methods for sample size determination: the one sample problem the two sample problem sample size for case-control studies sample size determination for cohort studies lot quality assurance sampling the incidence density sample size for continuous response variables sample size for sample surveys. Part 2 Foundations of sampling an...

To determine the effect of continuing medical education (CME) with and without a quality assurance component (CME+QA) on physician practices in the prevention of venous thromboembolism.
A communitywide study was performed in 15 short-stay hospitals in central Massachusetts. The study population included 3158 patients in acute-care hospitals with mu...

BACKGROUND: The purpose of the study was to examine overall differences and temporal trends therein between men and women regarding the incidence rates, in-hospital and long-term survival after initial acute myocardial infarction (AMI), and out-of-hospital deaths caused by coronary disease.
METHODS AND RESULTS: This nonconcurrent prospective study...

As part of a randomized trial that compared the effects of three physician-delivered smoking interventions on patients' long-term cessation rates, we examined factors associated with the extent of baseline cigarette smoking separately in 546 men and 715 women who were enrolled in this trial. Several baseline characteristics were significantly relat...

To investigate (1) the extent of agreement between what resident physicians and their patients report as having occurred in physician-delivered smoking interventions and (2) the ability of residents to effectively transmit information concerning smoking interventions to their patients.
A total of 263 patients and 91 residents in internal medicine o...

Relative excess risk due to interaction, the proportion of disease among those with both exposures that is attributable to their interaction, and the synergy index have been proposed as measures of interaction in epidemiologic studies. This paper presents the methodology for obtaining confidence interval estimates of these indices utilizing routine...

This study provides an estimate of the prevalence of risk factors for venous thromboembolism among hospital patients.
The presence of risk factors for venous thromboembolism was determined from a retrospective review of the medical records of 1,000 randomly selected patients in 16 acute care hospitals in central Massachusetts.
The most common risk...

To judge the effect on blood pressure, the ratio of polyunsaturated to saturated fatty acids (P:S) of foods served to students at two boarding high schools was modified alternately at each school for one school year. The average P:S of the diet of males increased from 0.53 to 0.93 during the intervention whereas among females it increased from 0.64...

The logistic regression model is being used with increasing frequency in all areas of public health research. In the calendar year 1989, over 30% of the articles published in the American Journal of Public Health employed some form of logistic regression modeling. In spite of this increase, there has been no commensurate increase in the use of comm...

To determine the rate of use of prophylaxis for venous thromboembolism in high-risk hospital patients.
A retrospective medical record review.
A community-wide study in 16 short-stay hospitals in central Massachusetts.
A total of 2017 patients with multiple risk factors for venous thromboembolism.
On the basis of age, length of hospitalization, and...

A community-wide study was conducted in 16 short-stay hospitals in metropolitan Worcester, Mass, to examine the incidence and case-fatality rates of deep vein thrombosis and pulmonary embolism in patients hospitalized between July 1, 1985, and December 31, 1986. The average annual incidence of deep vein thrombosis alone was 48 per 100000, while the...

A community-wide study was conducted in 16 short-stay hospitals in metropolitan Worcester, Mass, to examine the incidence and case-fatality rates of deep vein thrombosis and pulmonary embolism in patients hospitalized between July 1, 1985, and December 31, 1986. The average annual incidence of deep vein thrombosis alone was 48 per 100,000, while th...

Selection of a subset of meaningful covariates for a statistical model is an important and often time-consuming task in model building. J. F. Lawless and K. Singhal [ibid. 34, 318-327 (1978)] proposed a method for best subsets selection for nonnormal models. We develop a method for logistic regression that may be performed with any best subsets lin...

To judge the effect on blood pressure, sodium intake of students at two boarding high schools was reduced by 15-20% through changes in food purchasing and in preparation practices in the schools' kitchens. Students were not asked to change their usual eating habits. Each school served alternately as the control or intervention school for one school...

Data from the 1980 National Natality Survey by the National Center for Health Statistics were used to assess the relation of electronic fetal monitoring (EFM) during labor with cesarean section rates and neonatal morbidity and mortality. In univariate analyses, EFM was associated with higher cesarean section rates, lower five-minute Apgar scores, a...

The risk of adverse reproductive outcomes was examined among semiconductor manufacturers. Personal interviews were conducted with manufacturing workers, spouses of male manufacturers, and an internal comparison group of non-manufacturing workers. Elevated spontaneous abortion ratios were observed for females working in the "diffusion" (38.9%; relat...

This paper presents formulae for determining the number of subjects necessary, in either a case-control or a cohort study, to estimate the odds ratio or relative risk, respectively, to within a selected percentage (epsilon) of the true population value with some specified probability. This approach differs somewhat from previous comparable work tha...

Analysis of food diaries of 200 students in two boarding high schools indicated that 30% of their average daily sodium intake was contributed by bakery foods and ready-to-eat cereals. The next most important source of sodium (24%) was a category made up of food adjuncts, snack-type foods, soups, and beverages. The largest proportion of sodium in mo...

The distribution of the Hosmer-Lemeshow chi-square type goodness-of-fit tests (Čg, Ȟg) for the logistic regression model are examined via simulations designed to examine their behavior when most of the estimated probabilities are small or are expected to fall in a few deciles. The results of the simulations show statistic Čg should be used when the...

To investigate the frequency of physician delivery of advice to stop smoking and patient characteristics affecting whether
physicians deliver such advice, the authors surveyed 97 current cigarette smokers seen in two specialty and one general medicine
clinic at a university medical center. Approximately two thirds of the smokers reported ever havin...

To investigate those factors associated with patients' cigarette smoking status, 455 consecutive patients seen in two specialty clinics and one general medicine clinic at a university medical center were studied. Patient's age, sex, health status, and number of previous cessation attempts discriminated current from ex-smokers. A strong interaction...

We studied the effect of cod-liver oil on the development and progression of coronary artery disease in swine subjected to coronary balloon abrasion and fed an atherogenic diet for eight months. Sections from serial 3-mm segments of the coronary arteries were analyzed morphometrically in 7 pigs given a cod-liver-oil supplement and 11 control animal...