bluuebunny/crossref_metadata_2025_split huggingface dataset:
The use of logit models to investigate social and biological factors in infant mortality. III: Neonatal mortality
Authors: Machin D. , Murrells T. J. , Catford J. C. , Smith T. M. F. 
Published: April 2007

AbstractInfant mortality data for England and Wales, cross‐classified by mother's age, parity and social class have been published on two occasions, the first giving the relevant data for 1949/50, the second for 1975, some 25 years later. Published analyses of these separate data sets have been based on graphical and tabular analysis. This paper develops the methodology from an earlier paper by Murrells et al.1 to the analysis of the neonatal data.
A proposal for interpreting and reporting negative studies
Authors: Hauck Walter W. , Anderson Sharon 
Published: April 2007

AbstractAn issue of continuing interest is the interpretation and reporting of ‘negative’ studies, namely studies that do not find statistically significant differences. The most common approach is the design‐power method which determines, irrespective of the observed difference, what differences the study could have been expected to detect. We propose an alternative approach, the application of equivalence testing methods, where we define equivalence to mean that the actual difference lies within some specified limits. This approach, in contrast to the design‐power approach, provides a way of quantifying (with p‐values) what was actually determined from the study instead of saying what the study may or may not have accomplished with some degree of certainty (power). For example, a possible outcome of the equivalence testing approach is the conclusion at the 5 per cent level that two means (or proportions) do not differ by more than some specified amount.The equivalence testing approach applies to any study design. We illustrate the method with a cancer clinical trial and an epidemiologic case‐control study. In addition, for those studies in which one cannot specify limits a priori, we propose the use of equivalence curves to summarize and present the study results.
Sequential treatment allocation procedures in clinical trials‐with particular attention to the analysis of results for the biased coin design
Authors: Halpern Jerry , Brown Byron Wm. 
Published: April 2007

AbstractWe discuss the advantages and problems of using sequential allocation procedures for assigning treatments in a clinical trial. We use Monte Carlo methods to study the exact distribution of the fourfold chi‐squared statistic for the case of no stratifying variables except sequence of entry. We display situations in which the distribution is well‐approximated by the chi‐squared distribution or by Efron's adjusted chi‐squared and situations where these approximations fail. We provide suggestions for recognition and handling of situations in which both approaches fail.
Psychiatric admissions and choice of abortion
Authors: Andersen Per Kragh , Rasmussen Niels Kr. 
Published: April 2007

AbstractA statistical analysis is presented of the intensities of admissions to psychiatric hospitals among women in Denmark who either gave birth to a child in the year 1975 or had an induced abortion in the same year. The models used are time‐continuous Markov and semi‐Markov processes, and the methods employed include non‐parametric and semi‐parametric analysis of counting processes. The influence of prior psychiatric admissions on the choice of terminating the pregnancy with an induced abortion is also studied.
Case‐control studies and bayesian inference
Authors: Zelen M. , Parker R. A. 
Published: April 2007

AbstractWe outline the methods of Bayesian inference for applications to case‐control studies. These methods appear as the natural way of making inferences, since much of the controversy that surrounds a specific case‐control study is subjective. We derive conjugate prior distributions of exposure, posterior distributions of the ratio of the odds of being incident with a disease both with and without exposure to a potential causal agent, and convenient approximations. In particular, we show how one may carry out ‘case‐control studies’ without necessarily having a control group. We illustrate these ideas with the data that first showed the relationship betweenin uteroexposure to diethylstilbestrol and cancer of the vagina in young girls.
A statistical test for contact among individuals in an epidemic and a pattern among cases of acquired immune deficiency syndrome
Authors: Grimson Roger C. , Groshen Susan 
Published: April 2007

AbstractIn investigating an epidemic or outbreak of a disease in which patient contact (appropriately defined) is hypothesized to be a factor, investigators may ask patients to provide names of people with whom they have had contact. This paper provides statistical methods for assessing whether or not the number of named contacts who are themselves cases is significantly large. Survey data on the epidemiology of acquired immune deficiency syndrome illustrate the methods.
Allocation designs in cohort and case‐control studies
Authors: Moussa Mohamed A. A. 
Published: April 2007

AbstractFour unequal allocation designs for cohort and case‐control studies that incorporate cost and power are considered and compared with the equal allocation design, with the aim of providing researchers some flexibility in planning their studies. It is found that the type of design to be adopted depends on available resources and projected needs. In the case of tight expenditure, the minimized cost design is the optimal, whereas the maximized power design may be sought if the researcher intends to ensure a high chance of detecting any clinically significant relative risk of disease.
A clinical trial with an interim analysis
Authors: Chi P. Y. , Bristol D. R. , Castellana J. V. 
Published: April 2007

AbstractWe consider a fixed‐sample parallel‐group clinical trial with an interim analysis that tests Ho: μx = μy against H1: μx < μy. If we do not reject at the interim analysis, then the probability of making a type I error by rejecting Ho in favour of H2: μx > μy and the power at the final analysis are not appreciably affected by performing the interim analysis for certain relevant critical regions.
Statistical comparison of two handwashing protocols
Authors: Le Chap T. 
Published: April 2007

AbstractThis paper describes statistical procedures for use in an experiment that compares two handwashing protocols. The evaluation of a handwashing protocol entails collection of the wash effluent. Colony counts for the effluent reflect the number of flora removed by the wash protocol. The analysis aims to formulate and estimate an odds ratio that represents the relative efficacy of a test as compared with a standard protocol.
Sample sizes for phase II and phase III clinical trials: An integrated approach
Authors: Whitehead John 
Published: April 2007

AbstractIn this paper the following problem of clinical research is explored. Several potential new treatments are available for use against a certain disease. These are evaluated in a series of pilot studies which will constitute phase II clinical trials. The most promising will then be compared with a standard treatment in a phase III trial. Of interest will be the number of patients needed for the complete research programme, the proportions of these that should be involved in each phase, and the number of treatments which should be tried. Optimal strategies are found which maximize the probability that the overall programme identifies a treatment which is significantly better than the standard.
Life‐table methods for contraceptive research
Authors: Farley T. M. M. 
Published: April 2007

AbstractLife‐table methods used for the analysis and interpretation of contraceptive follow‐up studies differ from those used in other areas of medical research. The historical development of these methods in the contraceptive literature is outlined and the two main methods are discussed, compared and shown to differ mainly in their nomenclature; their results are very similar in practice. The daily life‐table method is simpler to apply and interpret, and facilitates analysis using the logrank statistic as well as powerful regression modelling techniques for survival data.
Intelligent dialogue based on statistical models of clinical decision‐making
Authors: McSherry D. M. G. 
Published: April 2007

AbstractThe independence Bayesian model has been used widely in computer programs designed to support clinical decision‐making. A reasoning strategy has been developed to enable these programs to conduct clinically pertinent dialogue and explain their reasoning. It has been implemented in a program for the diagnosis of acute abdominal pain based on the Bayesian model of de Dombal et al. Several features of the dialogue design have been adopted from artificial intelligence research, including shared initiative and critiquing. The program adopts a flexible goal‐driven strategy, attempting to confirm the clinician's diagnosis or rule out the likeliest alternative. Symptoms and signs are selected in order of their expected weights of evidence in favour of the hypothesized disease.
Partitioning methods for classification and decision making in medicine
Authors: Marshall R. J. 
Published: April 2007

AbstractThe use of partitioning methods for classification is discussed. A brief outline of the method of recursive partitioning is given and a note is made of some of its potential drawbacks. An alternative approach is outlined in which a particular class of dichotomous partitions is considered. The class incorporates prior knowledge concerning the nature of an association. Strategies to choose a partition from this class are suggested. The method is illustrated by an analysis of data from patients with gastrointestinal cancer and benign disease. A partition to discriminate between cancer and benign disease is obtained using symptoms, age and tumour marker data.
Some recent statistical analyses of two long‐term studies of exposure to ionizing radiation
Authors: Darby Sarah C. 
Published: April 2007

AbstractTwo long‐term studies of cancer mortality in populations exposed to high doses of ionizing radiation are described briefly. Statistical analysis plays a key role in establishing to what extent it is appropriate to generalize from the experience of these populations to that of other populations who have been exposed, usually at lower doses. Two examples of recent analyses are given. First, a detailed comparison of the cancer mortality experience in the two studies has been carried out; this has shown a high level of agreement between them. In the second example the relation between the radiogenic risk and the baseline age‐specific cancer risk in the two populations has been studied. Results are again in good agreement and show that for a group of epithelial tumours of non‐sex‐specific sites exposure to radiation multiplies the baseline risk.
Adjustment of risk ratios in case‐base studies (hybrid epidemiologic designs)
Authors: Greenland Sander 
Published: April 2007

AbstractThe recent growth of occupational epidemiology has led to a resurgence of interest in the hybrid epidemiologic study design of Kupper et al.,1 which has come to be termed a ‘case‐base’ or ‘case‐cohort’ design. This paper shows how the adjustment method for the risk ratio estimate given by Kupper et al. may have substantial bias, and also shows how one must modify conventional adjustment techniques (such as the Miettinen, Woolf and Mantel ‐Haenszel methods) when used with hybrid designs. This paper also provides the necessary modifications for tests and confidence intervals.
Applications of time‐series analysis: A case study on the impact of computer tomography
Authors: Tsouros Agis D. , Young Robert J. 
Published: April 2007

AbstractTime‐series techniques are applied to an analysis of the use of neurodiagnostic procedures in Athens, to evaluate the effect of the introduction of computer tomography. Results confirm the usefulness of such techniques, but illustrate the dependence of their successful application on the nature and quality of data.
Evaluation of the proportionate mortality index in the presence of multiple comparisons
Authors: Rockette Howard E. , Arena Vincent C. 
Published: April 2007

AbstractWe investigate the frequency in occupational studies of falsely identifying significantly elevated cause‐specific mortality in the presence of multiple comparisons. When one investigates a standard battery of causes of death, use of a standardized mortality ratio as a summary index results in an excessive experimental error rate, but one can control the error rate with use of standard procedures that limit the type I error. When a major disease category for an occupational cohort has a lower rate than expected, then with use of a proportionate mortality ratio as a summary index, the standard procedures for control of the type I error are inadequate. In this situation, use of a proportionate mortality ratio as a summary index is likely to result in the false identification of an excess cause‐specific mortality more often than previously acknowledged.
Robustness of the two independent samplest‐test when applied to ordinal scaled data
Authors: Heeren Timothy , D'Agostino Ralph 
Published: April 2007

AbstractOne may encounter the application of the two independent samplest‐test to ordinal scaled data (for example, data that assume only the values 0, 1, 2, 3) from small samples. This situation clearly violates the underlying normality assumption for thet‐test and one cannot appeal to large sample theory for validity. In this paper we report the results of an investigation of thet‐test's robustness when applied to data of this form for samples of sizes 5 to 20. Our approach consists of complete enumeration of the sampling distributions and comparison of actual levels of significance with the significance level expected if the data followed a normal distribution. We demonstrate under general conditions the robustness of thet‐test in that the maximum actual level of significance is close to the declared level.
Modified replacement randomization
Authors: Abel U. 
Published: April 2007

AbstractWe propose a slight modification of replacement randomization by imposing an imbalance criterion within a restricted range of patient entry numbers. The bound on imbalance is stated most simply in terms of the maximum allowable difference in treatment assignments at the end of the trial. For clinical trials in which two therapies are compared, we study, by means of computer simulations, the dependence of both selection bias and the mean number of randomization list replacements on the parameters defining the procedure.
Fitting nonlinear models with ARMA errors to biological rhythm data
Authors: Greenhouse Joel B. , Kass Robert E. , Tsay Ruey S. 
Published: April 2007

AbstractMany behavioural and physiological processes are periodic with a period of approximately 24 hours. For descriptive purposes, linear regression using a simple sinusoid with a fixed 24 hour period is sometimes an adequate tool for analysing data from such processes. Inference based on regression models under the assumption of independent and identically distributed errors, however, can often mislead seriously. In this paper we present a general class of models for fitting biological rhythms, with use of higher‐order harmonic terms of one or more unknown fundamentals and ARMA processes for the errors. We describe the procedures for model specification and estimation and give the theoretical justification for these procedures. Analysis of a series of human core body temperature illustrates the methodology.
Accumulating evidence from independent studies: What we can win and what we can lose
Authors: Light Richard J. 
Published: April 2007

AbstractWhen asking ‘what is known’ about a drug or therapy or program at any time, both researchers and practitioners often confront more than a single study. Facing a variety of findings, where conflicts may outweigh agreement, how can a reviewer constructively approach the task? In this discussion, I will outline some questions that can only be answered by examining a group of independent studies. I will also discuss some pitfalls that sometimes swamp the benefits we can gain from synthesis. Most of these pitfalls are avoidable if anticipated early in a review. The benefits of a quantitative review include information about how to match a treatment with the most promising recipients; increasing the statistical power to detect a significant new treatment; telling us when ‘contextual effects’ are important; helping us to assess the stability and robustness of treatment effectivenes; and informing us when research finds are especially sensitive to investigators' research design. The pitfalls include aggregating data from studies on different populations; aggregating when there is more than one underlying measure of central tendency; and emphasizing an average outcome when partitioning variance gives far more useful information.
Meta‐analysis of clinical trials as a scientific discipline. I: Control of bias and comparison with large co‐operative trials
Authors: Chalmers Thomas C. , Levin Howard , Sacks Henry S. , Reitman Dinah , Berrier Jayne , Nagalingam Raguraman 
Published: April 2007

AbstractMeta‐analysis is an important method of bridging the gap between undersized randomized control trials and the treatment of patients. However, as in any retrospective study, the opportunities for bias to distort the results are widespread. Attempts must be made to introduce the controls found in prospective studies by blinding the selection of papers and extraction of data and making blinded duplicate determinations. Informal and personalized methods of obtaining data are probably more liable to error and bias than employing only published data. Publication bias is a serious problem requiring further research. There also need to be more comparisons of meta‐analysed small studies with large co‐operative trials.
Methods for combining randomized clinical trials: Strengths and limitations
Authors: Demets David L. 
Published: April 2007

AbstractMethods for combining data from several studies exist and appear to be quite useful. None satisfactorily addresses the question of what studies should be combined. This issue is the most serious methodological limitation. Even studies with statistically significant interaction might still be combined if the effect were in the same direction. Thus, substantial scientific input is required as to what criteria must be met by each potential study. Much can be learned from combining or pooling data but it must be done cautiously. Pooling exercises do not replace well designed prospective clinical trials. Efforts for establishing basic design criteria to allow for multicentre and multicountry trials to be more easily combined might be useful.
Effects on overviews of early stopping rules for clinical trials
Authors: Green Stephanie J. , Fleming Thomas R. , Emerson Scott 
Published: April 2007

AbstractUse of inappropriate stopping rules for clinical trials results in an excess of false positive conclusions when no true survival differences exist. Overviews of such trials, however, consist mainly of trials which were not stopped early, plus a few of reduced sample size which were. Simulations confirm that the level of such an overview is minimally elevated. Additional follow‐up for survival further corrects the level. In fact, for individual trials conducted according to inappropriate rules, late tests have nearly correct level. On the other hand, publication bias (differential reporting of positive results) can substantially increase the level of an overview if only published studies are included.
Implications of overviews of randomized trials
Authors: Hennekens Charles H. , Buring Julie E. , Hebert Patricia R. 
Published: April 2007

AbstractMany randomized trials are of insufficient sample size to detect with adequate power the small to moderate effects that are most likely to occur. As a result, a single such trial can produce a null rinding that is, in fact, uninformative, but none the less is misinterpreted as demonstrating no effect. An overview considers all available trials and can increase the statistical power to detect an effect if present. Thus overviews can provide perhaps the most precise estimate of the magnitude of a treatment effect based on existing data. This may have implications for the formulation of public policy but certainly should influence the conduct and planning of randomized trials. Public policy may be influenced in circumstances where further trials are unlikely to be conducted. Overviews can also provide guidance as to whether changes in protocols of ongoing studies are recommended as a result of new evidence. Perhaps most importantly, overviews can provide information about whether additional trials are warranted, and, if so, the sample size that would be required to answer the research question definitively.
The relative efficiency of the sets and the cusum techniques in monitoring the occurrence of a rare event
Authors: Chen Rina 
Published: April 2007

AbstractThe efficiency of each of two methods for monitoring the occurrence of a rare event, the cusum, carried out monthly, and the sets techniques, was assessed by use of simulated datasets. The monthly cusum parameters used in this study were those recommended for monitoring of birth defects in a monthly analysis. The sets technique parameters, recommended for monitoring of low‐level epidemics, were adjusted to match the average interval between false alarms to the corresponding values observed for the monthly cusum technique. The results indicate that the relative efficiency of the two techniques depends on the baseline frequency of diagnoses. The sets technique is shown to be more efficient than monthly cusum when the number of cases expected in a year is no greater than five, but less efficient otherwise. In the former case, lengthening the interval between cusum analyses can make the cusum technique more efficient than the sets technique. This possibility deserves further exploration and could affect future recommendations.
A simple method of sample size calculation for unequal‐sample‐size designs that use the logrank or t‐test
Authors: Hsieh F. Y. 
Published: April 2007

AbstractThis paper presents a simple method of calculating sample sizes for unequal‐sample‐size designs with use of published tables applicable to equal‐sample‐size designs. The method applies to both the logrank test and the t‐test. For the power of logrank test, this paper compares the proposed method with existing methods and with the Monte Carlo simulation.
The analysis of a titration study
Authors: Chuang Christy 
Published: April 2007

AbstractFor analysis of data from a titration study, this paper adopts the idea of a life table analysis and utilizes a logistic linear dose–response model. The procedure uses iterated reweighted least‐squares to provide parameter estimates. Computation of the asymptotic covariance of the life‐table estimates of the response rates involves Greenwood's formula and a conditioning argument. A special case consists of examination of the covariance structure when no dropouts took place. Data from a titration study that investigated the efficacy of an anti‐hypertensive compound illustrate the procedure.