bluuebunny/crossref_metadata_2025_split huggingface dataset:
The number of partners and the probability of HIV infection
Authors: Eisenberg Bennett 
Published: April 2007

AbstractThis paper analyses the probability of contracting the AIDS virus in relation to the number of sexual contacts and the number of different partners. It is shown that in the case of a fixed number n of sexual contacts there is the following ranking from least risk to greatest risk: 1. a monogamous relationship with a non‐infected partner; 2. a monogamous relationship with a randomly selected partner; 3. a relationship with more than one randomly selected partners; 4. n randomly selected partners; 5. a monogamous relationship with an infected partner.
Policy implications of modelling of the AIDS epidemic
Authors: Brandt Edward N. 
Published: April 2007

AbstractHealth policy issues associated with AIDS are complex and controversial, including health care, research priorities, education, testing and confidentiality. Modelling may provide information relevant to their solution. Estimates of the future numbers of symptomatic persons and of the mix of severity are necessary for developing the capability to provide and fund health care services. Models may suggest other data needs and research directions. An important policy role of models is to permit evaluation of potential intervention steps and especially to project negative consequences. The critical contribution of models will be improved understanding of the dynamics of the AIDS epidemic.
A comparison of statistical methods for combining event rates from clinical trials
Authors: Berlin Jesse A. , Laird Nan M. , Sacks Henry S. , Chalmers Thomas C. 
Published: April 2007

AbstractWe compare two statistical methods for combining event rates from several studies. Both methods treat each study as a separate stratum. The Peto‐modified Mantel—Haenszel (Peto) method estimates a combined odds ratio assuming homogeneity across strata and provides a test for heterogeneity. The DerSimonian and Laird modified Cochran method (D&L) produces a weighted average of rate differences, where the weights allow for among‐study variability. We analyse 22 meta‐analyses from ten reports by both methods. The pooled estimates are divided by their standard errors to produce a Z‐statistic. A t‐test comparing Z‐statistics from all 22 studies suggests that the D&L method tends to be more conservative [d(Peto—D&L) = 0.29, t = 2.53, p = 0.02]. For a subset of 14 non‐heterogeneous studies, the difference is smaller and non‐significant (d = 0.09, t = 0.72, p = 0.49). The results from the methods correlate well (r = 0.66 for all 22 studies, r = 0.95 for 14 non‐heterogeneous studies). Thus, the presence of heterogeneity influences our conclusion. We discuss the statistical and scientific implications of these findings.
Factorial designs in clinical trials: The effects of non‐compliance and subadditivity
Authors: Brittain Erica , Wittes Janet 
Published: April 2007

AbstractFactorial designs in clinical trials allow for the study of several medical treatments simultaneously. This paper distinguishes among different types of settings in which factorial designs are useful. For the experiment that involves investigation of several new or untested therapies, we introduce a model that incorporates rates of non‐compliance to therapy as well as various degrees of subadditivity of treatment effects. We compare the operating characteristics of the factorial under this model with those of competing designs and show that a modest negative interaction can considerably diminish the power to detect treatment effects in the factorial even in cases that have little power to detect this interaction. We urge, therefore, that designers of clinical trials with factorial layouts posit realistic estimates of interactions among treatments in order to assure adequate power to detect beneficial effects of treatment.
Issues in analysing the effects of occupational exposure to low levels of radiation
Authors: Gilbert E. S. 
Published: April 2007

AbstractA major objective of studying populations exposed to low levels of radiation is provision of direct assessment of the adequacy of estimates of health risks obtained by extrapolation of data on populations exposed at high levels. Meeting this objective requires the use of statistical methods that fully utilize available exposure measurements, and that consider the extensive body of prior knowledge regarding radiation‐induced health effects. This paper describes various methods of analysis and illustrates the methods with data on workers at the Hanford Site. Special problems are discussed, with attention to comparability of estimates and confidence limits with those obtained from extrapolation.
Variance estimation for medical decision analysis
Authors: Katz Barry P. , Hui Siu L. 
Published: April 2007

AbstractWe have derived the variance of an expected utility for a probability tree in medical decision analysis based on a Taylor series approximation of the expected utility as a function of the probability and utility values used in the decision tree. The resulting variance estimate is an algebraic expression of the variances associated with the probability and utility estimates used. We also derive expressions for the case where the input parameter estimates are not independent. We discuss the choice of input parameters and their variance estimates and give an example that compares two protocols for the treatment of chlamydial infection.
An application of a mathematical model to adjust for time lag in case reporting
Authors: Lui Kung‐Jong , Rudy Richard K. 
Published: April 2007

AbstractIn a dynamic, fluctuating surveillance system, the time lag of case reporting often causes an artificial plateau in an epidemic curve. Arbitrarily ignoring data reported in the most recent period to avoid this bias causes the loss of valuable information. In this report, we propose an application of a mathematical model to adjust for the underreporting bias owing to the time lag of the reporting process. We present an example using the acquired immunodeficiency syndrome incidence data for the homosexual group in the San Francisco surveillance system to illustrate and evaluate prospectively this proposed technique. The results show that the adjusted incidence obtained with the model agrees reasonably well with the true incidence, except for the last month of the period under consideration.
Monitoring data quality through comparisons between data systems
Authors: Massey James T. , Hoffman Keith L. 
Published: April 2007

AbstractSince its creation in 1960, the National Center for Health Statistics (NCHS) has placed a high value on the quality of the information and statistics collected and published by its data systems. An important component of a comprehensive data quality monitoring system for a statistical agency such as NCHS is the comparison of statistics between data systems. Between‐data‐systems comparisons are used to monitor the consistency and comparability of statistics across data systems and between NCHS data systems and outside sources of data. This paper focuses on between‐data‐systems comparisons and describes a number of methodological analyses that can be used to evaluate data quality. The methodological analyses presented include the evaluation of time trends, the estimation of survey method effects, the evaluation of response error, the measurement of definitional and concept effects, and the detection of inconsistencies between data systems. The paper concludes with a discussion of the complexities of the between‐data‐systems comparisons and an assessment of the net benefits from such comparisons.
Estimating trends in the effectiveness of seat belts in saving lives, 1975–1985
Authors: McGee Daniel L. , Rhodes Phil 
Published: April 2007

AbstractWe examine the effectiveness of seat‐belt systems for preventing mortality in automobile crashes. In particular, we examine whether seat‐belt effectiveness has been constant over this period and conclude that there has been a trend toward an increased effectiveness of seat‐belt systems. The relative odds of death associated with wearing seat belts dropped from 0.80 in 1975 to 0.34 in 1985. This trend results from improvements in both the type and design of seat belts and from additional design changes, such as padded dashboards and collapsible steering columns, that protect occupants at the time of collision.
Flexible regression models with cubic splines
Authors: Durrleman Sylvain , Simon Richard 
Published: April 2007

AbstractWe describe the use of cubic splines in regression models to represent the relationship between the response variable and a vector of covariates. This simple method can help prevent the problems that result from inappropriate linearity assumptions. We compare restricted cubic spline regression to non‐parametric procedures for characterizing the relationship between age and survival in the Stanford Heart Transplant data. We also provide an illustrative example in cancer therapeutics.
The analysis of titration studies in phase III clinical trials
Authors: Shih Weichung Joseph , Gould A. Lawrence , Hwang Irving K. 
Published: April 2007

AbstractClinical trials commonly employ the titration design for certain drugs such as antihypertensives. In a Phase III trial the design has purposes distinct from those of a Phase I or II trial, as well as from those of a trial with a parallel design. In this paper we compare the titration design with the usual parallel design in their respective purposes for Phase III trials, explore the relevant questions addressed, and examine typical data from such trials. We also discuss work which focuses primarily on the Phase I or II titration trials. We formulate the problem in the framework of a one‐way contingency table augmented with incomplete data and obtain the maximum likelihood estimates of the parameters and their estimated variances/covariances via the EM algorithm. An example of a Phase III study of an antihypertensive agent illustrates the proposed procedure.
Assessing diagnostic tests by a strictly proper scoring rule
Authors: Linnet Kristian 
Published: April 2007

AbstractEvaluation of univariate quantitative diagnostic tests by strictly proper scoring rules is considered as an alternative to the traditional error rate measures. In principle, the posterior probability of disease as a function of the test value is estimated from training observations, and subsequently the score is assessed on a set of test samples. The same subjects may serve as training and test samples when the bootstrap procedure is applied for estimation of standard errors and correction of bias. The method is demonstrated using serum bile acids and bilirubin in patients with liver disease. The power for comparison of scores from two tests is compared with that from error rate measures for some typical situations.
Sample size tables for logistic regression
Authors: Hsieh F. Y. 
Published: April 2007

AbstractSample size tables are presented for epidemiologic studies which extend the use of Whittemore's formula. The tables are easy to use for both simple and multiple logistic regressions. Monte Carlo simulations are performed which show three important results. Firstly, the sample size tables are suitable for studies with either high or low event proportions. Secondly, although the tables can be inaccurate for risk factors having double exponential distributions, they are reasonably adequate for normal distributions and exponential distributions. Finally, the power of a study varies both with the number of events and the number of individuals at risk.
A method for the evaluation of dose‐toxicity relationships in clinical trials
Authors: Mather Frances J. , Simon Richard M. , Clark Gary M. , Von Hoff Daniel D. 
Published: April 2007

AbstractThis paper considers a proportional hazards model that describes the relationship between time‐dependent cumulative dose of drug and development of toxicity. We estimate probabilities of developing toxicity in both the presence and the absence of competing risks and provide variances for the latter case. Mitoxantrone data collected in Southwest Oncology Group studies illustrate the methods.
Estimability and estimation of excess and etiologic fractions
Authors: Robins James M. , Greenland Sander 
Published: April 2007

AbstractThis paper describes conditions under which epidemiologic data can provide estimates of the excess fraction (proportionate increase in caseload due to an exposure) and the etiologic fraction (fraction of cases caused by exposure). The excess fraction can be estimated under essentially the same conditions often cited for general study validity. In contrast, estimation of the etiologic fraction will usually require very specific nonidentifiable assumptions about exposure action and interactions, although one can derive simple lower and upper bounds for the fraction from survival comparisons. Since the etiologic fraction is equivalent to the probability of causation, our results have implications for injury compensation in lawsuits involving the probability of causation.
Statistical comparison of ligand‐binding kinetics
Authors: Cologne John B. , Mendelman Paul M. , Chaffin Donald O. 
Published: April 2007

AbstractWe describe the application of generalized linear model methodology to the problem of testing differences among ligand‐receptor interactions, and show that the method is analogous to weighted least squares regression methodology and F tests familiar to many investigators. The method accommodates incomplete block designs so that one can obtain kinetic parameter estimates directly comparable among samples analysed on incompletely overlapping sets of experimental runs. We demonstrate the method with data that compare saturation kinetics for a single penicillin‐binding protein in isogenic ampicillin susceptible and resistant bacteria.
Effect of unequal censoring on the size and power of the logrank and Wilcoxon types of tests for survival data
Authors: Beltangady Mohan S. , Frankowski Ralph F. 
Published: April 2007

AbstractThis paper examines the effect of random unequal censoring on the size and power of two‐sample logrank and Wilcoxon types of tests for comparing two survival distributions by simulation with small samples from censored exponential distributions. We compared equal‐sized samples of n = 8, 16, and 32 with 1000 (size) and 500 (power) simulation trials for 16 combinations of the censoring proportions of 0, 20, 40, and 60 per cent in each of the two samples. For n = 8, the asymptotic normality (AN), Peto‐Peto, and the two Wilcoxon‐type tests performed at nominal 5 per cent size expectations, but the Mantel test exceeded the 5 per cent size acceptance region in 6 of 16 censoring combinations. For n = 16 and 32, all tests showed proper size, with the Peto‐Peto test being most conservative in the presence of unequal censoring. We compared powers of all tests for exponential hazard ratios of 1·4 and 2·0. The Mantel test showed 90 to 95 per cent power efficiency relative to the parametric AN test. Both Wilcoxon tests performed identically and had the lowest relative power of all tests examined but appeared most robust to the differential censoring patterns studied. A modified version of the Peto‐Peto test showed power comparable to the Mantel test.
A review of methods for misclassified categorical data in epidemiology
Authors: Chen T. Timothy 
Published: April 2007

AbstractMisclassification introduces errors in categorical variables. This paper presents a review of methods for misclassified categorical data in epidemiology. Different sampling schemes for a 2 × 2 × 2 table and methods of analyses will be discussed first. A misclassification matrix is defined, and the usual misclassification models will be shown to be a subclass of log‐linear models. Well‐known results on a 2 × 2 table with misclassification and recent results on a 2 × 2 × 2 table are then reviewed. Finally two methods of adjusting for misclassification will be given. The first method assumes a known misclassification matrix, and the second method uses subsampling to estimate the misclassification matrix. The analysis is based on a recursive system of log‐linear models: first determine a misclassification model, then select a model for the correctly classified variables. The methods are illustrated by data from traffic safety research on the effectiveness of seatbelt use in reducing injuries.
Indoor air pollution and pulmonary performance: Investigating errors in exposure assessment
Authors: Hasabelnaby Nancy A. , Ware James H. , Fuller Wayne A. 
Published: April 2007

AbstractWe use pulmonary function measurements on pre‐adolescent children and indoor air pollution measurements in the homes of these children to illustrate estimation techniques for linear regression models containing independent variables measured with error. In our data set, replicate measures of indoor air pollutant concentrations provide one method of estimating measurement error variances. Surrogate information in the form of cigarettes smoked is also available for the pollutant of interest. Several estimation procedures are presented, and we combine two estimators, one based on surrogate information and one based on replication information, using generalized least squares.
Analysis of case‐control data with covariate measurement error: Application to diet and colon cancer
Authors: Armstrong Ben G. , Whittemore Alice S. , Howe Geoff R. 
Published: April 2007

AbstractWe propose a method for estimating odds ratios from case‐control data in which covariates are subject to measurement error. The measurement error may contain both a random component and a systematic difference between cases and controls (recall bias). A multivariate normal discriminant analysis model is assumed. If the distribution of measurement error is known, then a simple correction to naive (biased) estimates of odds ratios from logistic regression of disease on fallible measurements of covariates removes bias. The same correction yields confidence intervals and significance tests. We apply the proposed methods to data from a case‐control study of colon cancer and diet.
The ordered logistic regression model in psychiatry: Rising prevalence of dementia in old people's homes
Authors: Ashby Deborah , West Christopher R. , Ames David 
Published: April 2007

AbstractOrdered logistic regression is an extension of binary logistic regression, and is particularly well suited to the analysis of many psychiatric scores. Its use is demonstrated in a pair of linked cross‐sectional surveys of dementia in residents of old people's homes, first to model the association of dementia with demographic characteristics, and then to explore possible reasons for a rise in the prevalence of dementia in the homes over a four‐year period.
Estimation of temporal effects in treatment‐induced second cancer
Authors: Kaldor J. M. , Day N. E. 
Published: April 2007

AbstractCancer chemotherapy has been remarkably successful in the treatment of several types of malignancies, but has also been demonstrated to cause leukaemia and perhaps other cancer in long‐term survivors. Radiotherapy also carries a carcinogenic risk. A large case‐control study of second cancer has been carried out, with the aim of quantifying the risk due to chemotherapy and radiotherapy. One of the most important goals of this study is the estimation of the temporal pattern of risk following chemotherapy. Methods are presented for modelling risk as a function of type of treatment and the interval since reatment. The methods are applications of generally available linear regression programs for epidemiological data, and could be equally well applied to studies of occupationally induced cancer.
A measure of similarity for response curves based on ranks
Authors: Schulgen Gabi 
Published: April 2007

AbstractA measure of similarity for response curves is presented and its potential use is discussed. The distribution of a suitable test statistic for testing the independence of the course of two curves is derived. The method proposed is compared with other proposals in the literature for the analysis of paired response curves. A study on the quality of life of patients with acute heart failure is used as an example.
The performance of the two‐stage analysis of two‐treatment, two‐period crossover trials
Authors: Freeman P. R. 
Published: April 2007

AbstractIn the two‐treatment, two‐period crossover trial, patients are randomly allocated either to one group that receives treatment A followed by treatment B, or to another group that receives the treatments in the reverse order. Grizzle first proposed a two‐stage procedure for analysing the data from such a trial. This paper examines the long‐run sampling properties of this procedure, in terms of mean square error of point estimates, coverage probability of confidence intervals and actual significance level of hypothesis tests for the differences between the effects of the two treatments. The advantages of incorporating baseline observations into the analysis are also explored. Because the preliminary test for carryover is highly correlated with the analysis of data from the first period only, actual significance levels are higher than nominal levels even when there is no differential carryover. When carryover is present, the nominal level very seriously understates the actual level, and this becomes even worse when baseline observations are ignored. Increasing sample size only exacerbates the problem since this adverse behaviour then occurs at smaller values of the carryover effect. It is concluded that the two‐stage analysis is too potentially misleading to be of practical use.
Grading of images in a clinical trial
Authors: Seigel Daniel , Milton Roy C. 
Published: April 2007

AbstractWe developed a computer model to compare the power in clinical trials that use either of two grading schemes for objectively recorded dependent variables. The example we use is an eye lens photo. The first grading system consists of side by side comparison of the before and after treatment photos; the second involves separate grading of the two photos. This modelling experience suggests that separate grading may often yield more power than side by side comparison, and offers other advantages as well. For applications in which grading error is considerably smaller in the side by side method, power may be markedly better. Most importantly, strong prejudice in favour of one or the other approach in all situations seems unwarranted.
A comparison of tests of homogeneity of odds ratios inK2 × 2 tables
Authors: Paul S. R. , Donner A. 
Published: April 2007

AbstractWe conducted a simulation study to determine the performance of nine procedures for testing the homogeneity of odds ratios inK2 × 2 contingency tables. We recommend Tarone's approximate score test, based on the Mantel—Haenszel estimator of the common odds ratio, for use in practice. We also recommend a non‐iterative statistic developed by Gart and based on the modified Woolf estimator of the common odds ratio for very large samples in balanced or mildly unbalanced designs. We base our recommendation of a statistic on its performance in terms of size and power in comparison with the other statistics considered.
The case of gissi in changing the attitudes and practice of Italian cardiologists
Authors: Tognoni Gianni , Franzosi Maria Grazia , Garattini Silvio , Maggioni Aldo , Lotto Antonio , Mauri Francesco , Rovelli Fausto 
Published: April 2007

AbstractThis report first describes the efficiency achieved by a large scale clinical trial (GISSI), which is widely recognized as having made an important contribution to the therapy of AMI, and second emphasizes how a comprehensive research project based upon an innovative clinical trial methodology can influence the attitude and the scientific productivity of a professional community operating within a national health system. To understand the methodology of GISSI, one must appreciate both the cultural and institutional setting in which the first GISSI trial took place as well as the strong economic and scientific expectation surrounding the second GISSI trial.