bluuebunny/crossref_metadata_2025_split huggingface dataset:
The analysis of neuronal discharge sequences: Change‐point estimation and comparison of variances
Authors: Commenges Daniel , Seal John 
Published: April 2007

AbstractA key problem in neurophysiology is to determine whether, after presentation of a stimulus, there has been a modification in the discharge of a recorded neuron and if so, an attempt is made to estimate the latency of the response. The estimation problem can be considered as that of the estimation of a change‐point in a sequence of random variables. The gamma distribution is adequate to model the distribution of intervals between action potentials for different types of neurons. Simulations show that the maximum likelihood estimator based on this model is efficient and robust.An additional problem, in the case of experiments in which a movement follows the stimulus, is to determine whether a response is related to the stimulus or to the movement. A test based on the comparison of marginal scales of a bivariate distribution is proposed. The whole procedure has been tested in simulation and with real examples.
The 2 × 2 factorial design: Its application to a randomized trial of aspirin and U.S. physicians
Authors: Stampfer Meir J. , Buring Julie E. , Willett Walter , Rosner Bernard , Eberlein Kimberly , Hennekens Charles H. 
Published: April 2007

AbstractThe 2 × 2 factorial design calls for randomizing each participant to treatment A or B to address one question and further assignment at random within each group to treatment C or D to examine a second issue, permitting the simultaneous test of two different hypotheses. This design can increase the efficiency of large‐scale clinical trials. The Physicians' Health Study, a randomized trial of aspirin and beta‐carotene among U.S. physicians, illustrates some features and potential problems in the design and analysis of a factorial trial. The most common concern, interaction between treatments, is generally an advantage rather than a limitation of this design. Although such interactions are relatively uncommon, this design provides a means to measure an effect which otherwise might not be apparent. If the interaction is sufficiently severe, however, then loss of power is possible.
Power, sample size and smallest detectable effect determination for multivariate studies
Authors: Greenland Sander 
Published: April 2007

AbstractThis paper discusses some general methods for determining approximate power, sample size, and smallest detectable effect for studies of multiple risk factors. These methods are based on standard large‐sample formulae for determining the power of chi‐square tests, and emphasis is given to determinations for Pearson χ2 tests in multiway contingency tables. The methods are illustrated in application to the design of a clinical trial of the preventive effect of α‐tocopherol, ascorbic acid and β‐carotene on colon polyp recurrence, and a case‐control study of the joint effect of smoking and asbestos exposure on lung cancer incidence.
Formulae for cause‐deleted life tables
Authors: Smith David P. 
Published: April 2007

AbstractThe medical and demographic literature contain two popular formulae for the construction of cause‐deleted life table lx values, one developed for applications in follow‐up studies and the other for cross‐sectional studies. It turns out that for both types of applications one of the two formulae is virtually always of better quality than the other. A formula developed by Keyfitz and Frauenthal5 is usually better than either.
Comparison of ascertainment‐bias correction schemes for pedigrees ascertained through multiple probands
Authors: Majumder Partha P. 
Published: April 2007

AbstractAssessing the genetic causation of a disease, which is of prime importance in medical genetics, is usually done by analysing pedigree data. When gathering such data, it is often more practical to adopt a non‐random sampling strategy. However, unless suitable corrections for non‐random sampling are made at the time of data analysis, inferences may be grossly affected. For pedigree data ascertained through multiple probands, various correction schemes have been suggested, although the efficiencies of these schemes are unknown. This paper compares such schemes, using Monte Carlo simulation techniques, under a simple genetic model, for pedigrees of fixed sizes and structures and for probands of two types of relationship‐parent‐offspring, and a pair of siblings. It is found that gene frequencies are grossly overestimated and the penetrance value of heterozygotes slightly underestimated whether or not any correction for non‐random sampling of pedigrees is made. Knowledge of the population value of the gene frequency improves the estimate of the penetrance parameter.
Comparative analysis of two rates
Authors: Miettinen Olli , Nurminen Markku 
Published: April 2007

AbstractIn this paper, we examine comparative analysis of rates with a view to each of the usual comparative parameters‐rate difference (RD), rate ratio (RR) and odds ratio (OR)‐and with particular reference to first principles. For RD and RR we show the prevailing statistical practices to be rather poor. We stress the need for restricted estimation of variance in the chi‐square function underlying interval estimation (and also point estimation and hypothesis testing). For RR analysis we propose a chi‐square formulation analogous to that for RD and, thus, one which obviates the present practice of log transformation and its associated use of Taylor series approximation of the variance. As for OR analysis, we emphasize that the chi‐square function, introduced by Cornfield for unstratified data, and extended by Gart to the case of stratified analysis, is based on the efficient score and thus embodies its optimality properties. We provide simulation results to evince the better performance of the proposed (parameter‐constrained) procedures over the traditional ones.
Assessing apparent treatment—covariate interactions in randomized clinical trials
Authors: Byar David P. 
Published: April 2007

AbstractIn the context of clinical trials, a qualitative treatment—covariate interaction occurs when a patient's preferred treatment depends on his covariates. In this paper I review the nature and interpretation of various kinds of interactions, compare the use of overall tests for interaction to subset analysis, present some examples of apparent treatment‐covariate interactions that have arisen in actual randomized clinical trials, and discuss some recent work by others related to significance testing, estimation and assessment of apparent treatment—covariate interactions.
Prognostic factors for stagei melanoma of the skin: A review
Authors: Cascinelli N. , Marubini E. , Morabito A. , Bufalino R. 
Published: April 2007

AbstractThe prognosis of melanoma of the skin has been investigated in many studies. In this report papers on the prognosis of stage I melanoma published since 1975 in the leading oncology journals have been reviewed. Further the data collected by the WHO Collaborating Centre for Evaluation of Methods of Diagnosis and Treatment of Melanoma are analysed, and the results compared with those of other series. Three factors emerge as clearly influencing prognosis: sex, maximum tumour thickness and ulceration. The role of other factors and particularly that of an interaction between tumour thickness and ulceration conjectured by some authors remains questionable.
Critical discussion of the assessment of a three‐stage prognostic classification for chronic lymphocytic leukemia
Authors: Chastang Claude , Travade Philippe , Auquier Ariane 
Published: April 2007

AbstractA study of the prognosis of two series of chronic lymphocytic leukemia (CLL) patients (99 from a retrospective series and 196 from a prospective series) has led us to propose a three‐stage classification (A, B, C), requiring only a clinical examination and a haemogram.For stage A patients (comprising 50% of the CLL patients), survival rates are similar to those in the French general population of the same age and sex; median survival time is six years for stage B patients (comprising 35% of CLL) and two years for stage C patients (comprising 15%).Several methodological difficulties were encountered with the data and the statistical strategy, and these are discussed. The staging system has been justified, since the results have now been confirmed in four other series, totalling 611 CLL patients.
Comparison of the mortality of a cohort with the mortality of a reference population in a prognostic study
Authors: Hill Catherine , Laplanche Agnes , Rezvani Ali 
Published: April 2007

AbstractIt is standard practice in epidemiological studies to compare the observed mortality of a cohort to the mortality expected in a reference population of the same age and sex distributions computed from national statistics. The same methods can be used in a prognostic study where the effects on survival of potential prognostic factors are studied in a cohort of patients with a given disease. Writing the hazard function in the cohort as the product of the hazard function in the reference population and a function of some characteristics of the patients, one can derive simple estimates and statistical tests of the standardised mortality ratios (Breslow et al.1). The study of a cohort of patients with thyroid cancer will provide an example.
Computer assistance for C.T. scan interpretation and cerebral disease diagnosis
Authors: Teather D. , Morton B. A. , du Boulay G. H. , Wills K. M. , Plummer D. , Innocent P. R. 
Published: April 2007

AbstractThis paper describes the development and use of a system to aid in the radiological interpretation of C.T. scan images of patients with cerebral disease. The system is able to provide guidance, both on diagnosis and the need for further scan investigations. Explanation and help facilities, similar to those found in certain rulebased expert systems, are available on demand. Diagnostic and other advice is, however, based on hard statistical data. The scan interpretation and diagnostic system offers important benefits in the training of less experienced radiologists.
Knowledge based expert systems for medical diagnosis
Authors: Torasso Pietro 
Published: April 2007

Abstract‘Knowledge based expert systems’ have been developed in the last decade for many different applications by adopting artificial intelligence techniques. The paper discusses the main characteristics of the expert systems devoted to medical diagnosis (knowledge representation, explanation capability, inexact reasoning) and addresses some of the limitations (mainly system validation and knowledge acquisition). Finally the paper sketches the overall organization of an expert system devoted to the evaluation of liver function.
Latent class analysis in chronic disease epidemiology
Authors: Kaldor John , Clayton David 
Published: April 2007

AbstractLatent class analysis provides a useful framework for the analysis of epidemiological data which may have been mismeasured. In this paper, the latent class model is described in the context of logistic regression with categorical variables, and some examples of its application are provided. In particular, it is shown that adjustment for a misclassified confounding variable can be greatly improved by using the methods presented.
Hypothesis testing in the polychotomous logistic model with an application to detecting gastrointestinal cancer
Authors: Marshall R. J. , Chisholm E. M. 
Published: April 2007

AbstractWe discuss the use of the trichotomous logistic model to discriminate between patients with gastrointestinal(GI) cancer, patients with benign GI disease and ‘normal’ subjects, using symptoms and the concentrations of some serum proteins that are potentially indicative of malignancy as covariates. A parsimonious model can be obtained by invoking an indistinguishability hypothesis which is appropriate when a covariate is considered to have no predictive value between categories. It is shown that the polychotomous model can be re‐parameterised under the null hypothesis to give a ‘reduced form’, which can be fitted by maximum likelihood. The validity of the use of the same methods for retrospective sampling is discussed. The approach is illustrated by the development of a logistic model to identify symptomatic and asymptomatic subjects with a high risk of GI cancer.
Assessment of some risk factors for hepatocellular carcinoma: A case control study
Authors: Filippazzo M. G. , Aragona E. , Cottone M. , Dardanoni G. , Lanzarone F. , Marenghini A. , Patti C. , Sciarrino E. , Simonetti R. , Tine F. , Pagliaro L. 
Published: April 2007

AbstractA case‐control study of risk for hepatocellular carcinoma (HCC) was carried out in our Department from December 1980 to December 1983. One hundred and twenty consecutive inpatients with HCC were compared with 360 controls pair‐matched by sex and age (within years). For each case three different controls were selected from inpatients at the same hospital: one patient with liver cirrhosis; one patient with solid tumor and one patient with chronic illness other than neoplasm or liver disease. We report here the results on alcohol consumption, smoking habit and hepatitis B virus infection. The risk factors investigated are distributed similarly in HCC and cirrhosis. The prevalence of alcohol abuse in HCC is similar to that in cirrhosis and is significantly higher than in other neoplastic or otherwise chronically ill patients (odds ratio 2.3 and 3.2 respectively). Thus alcohol abuse is probably a risk factor for HCC as a cause of cirrhosis.Smoking habits were similar among the various disease groups and independent of alcohol consumption. The prevalence of heavy smoking was comparable in cases and controls. HbsAg negative‐HCC with an ultrasonographic pattern of ‘diffuse’ alteration was more frequent in heavy smokers.
Comparison of three devices for measuring blood pressure
Authors: Bassein Leona , Borghi Claudio , Costa Francesco Vittorio , Strocchi Enrico , Mussi Alessandra , Ambrosioni Ettore 
Published: April 2007

AbstractBlood pressure measurement with two automatic devices, Dinamap 845 and Sentry, was compared with the standard mercury sphygmomanometer, by means of a 3‐period crossover experiment. Both automatic devices read diastolic pressure considerably lower than the mercury sphygmomanometer (about 7 mmHg on average); agreement was better for systolic pressure. Device differences in individual patients were often much higher. To assess the patient's emotional pressor response during manual measurement, Dinamap was used to monitor blood pressure before, during and after measurement with the mercury sphygmomanometer. No rise in pressure was found. It is concluded that the three devices can often give different values, and that the physician's involvement cannot explain these differences.
Are routine clinical chemistry analyses ‘in control’ according to shewhart's technique?
Authors: Boerma G. J. M. 
Published: April 2007

AbstractThe clinical laboratory routinely uses quality control (QC) procedures. The Shewhart technique of charting control data, introduced in 1950, is usually applied in a much simplified manner. This reduces its power to distinguish between random errors and errors due to assignable causes. In a comparison of one of our routine charting procedures with a correct Shewhart procedure we checked 23 chemical tests. We found that using the latter ‘a stable system of chance causes’ did not exist for 6 tests. Both control procedures agreed well on the evaluation of reproducibility. For three of the tests, albumin, urea and uric acid, the instability was not detected by the routine procedure.Although charting of group means (x̄i) and ranges (Ri) more readily detected instability, it did not lead to a negation of the practical utility of our patient data.
The pattern of ischemic heart disease 1931–1980
Authors: Smith David P. , Slater Carl 
Published: April 2007

AbstractThe rise in ischemic heart disease in the U.S. after 1920 has been described in the literature both as a 20th century epidemic and as an artifact of the decline of competing causes of death, particularly the infectious, parasitic and diarrheal diseases. Shifting medical terminology and occasional major revisions in cause of death codes have aggravated efforts to resolve the debate. Through regression analysis and ordinary and cause‐deleted life tables we trace the course of the disease. The accumulated evidence points to a major epidemic but one largely confined to males. Reversals in patterns are now beginning.
Selecting risk factors: A comparison of discriminant analysis, logistic regression and cox's regression model using data from the tromsø heart study
Authors: Brenn Tormod , Arnesen Egil 
Published: April 2007

AbstractFor comparative evaluation, discriminant analysis, logistic regression and Cox's model were used to select risk factors for total and coronary deaths among 6595 men aged 20–49 followed for 9 years. Groups with mortality between 5 and 93 per 1000 were considered. Discriminant analysis selected variable sets only marginally different from the logistic and Cox methods which always selected the same sets. A time‐saving option, offered for both the logistic and Cox selection, showed no advantage compared with discriminant analysis. Analysing more than 3800 subjects, the logistic and Cox methods consumed, respectively, 80 and 10 times more computer time than discriminant analysis. When including the same set of variables in non‐stepwise analyses, all methods estimated coefficients that in most cases were almost identical. In conclusion, discriminant analysis is advocated for preliminary or stepwise analysis, otherwise Cox's method should be used.
Assessing the adequacy of the logistic regression model for matched case‐control studies
Authors: Moolgavkar Suresh H. , Lustbader Edward D. , Venzon David J. 
Published: April 2007

AbstractWe apply results for the detection of outliers in logistic regression to the analysis of matched pairs data and illustrate the techniques with data from a matched pairs study of the relationship between iron‐binding proteins and mortality in the Solomon Islands. Although the study includes 90 matched pairs, the conclusions change substantially with deletion of one or two pairs. Thus, even with reasonably large data sets, single observations may have a great impact on the results of an analysis. The identification of influential observations should constitute part of the analysis of matched case‐control data.
Using test‐retest reliability data to improve estimates of relative risk: An application of latent class analysis
Authors: Clayton David 
Published: April 2007

AbstractThe paper discusses the problem of interval estimation for the relative risk when some test‐retest data are available on random subsamples drawn from case‐control studies. It is shown that, although the upper portion of the interval may be very wide indeed, the lower bound of the interval estimate may be improved considerably by the collection of even modest amounts of repeat measurements.
The cusum test of homogeneity with an application in spontaneous abortion epidemiology
Authors: Levin Bruce , Kline Jennie 
Published: April 2007

AbstractWe test the hypothesis of homogeneity over time in the rate of an event with a modification of Page's cumulative sum (cusum) procedure. The modification draws on an indifference zone approach to testing that is well suited to the epidemiologic study of retrospective data. We provide procedures for evaluating the significance level of the largest observed cusum value occurring in a sequence of fixed length. We draw inferences unconditionally with a known baseline rate of the event, and conditionally on observed margins with unknown baseline rate. Data collected over a five year period from one New York City hospital serve to illustrate the modified cusum test in a study of fluctuations in the proportions of chromosomally normal, trisomic, X‐monosomic and triploid spontaneous abortions.
The value of specialized tests in studies where ordered group means are expected
Authors: Shirley Eryl A. C. 
Published: April 2007

AbstractThe performances of three tests for ordered means (Bartholomew's, Williams' and a modified method of least significant differences) are compared with the performances of more general multiple comparison procedures. The tests are assessed using simulated data representing various patterns of results from a toxicological study with one (zero dose) control group and three treatment groups. The specialized tests are considerably more powerful than the general tests and their application is recommended whenever ordered group means are expected.
Optimal designs for clinical trials with dichotomous responses
Authors: Berry Donald A. , Pearson Larry M. 
Published: April 2007

AbstractWe consider two‐stage designs for clinical trials that involve two treatments with dichotomous responses. The first is the information‐gathering stage; the treatment chosen as the better from first stage and prior data is used exclusively in the second stage. Determination of treatment allocation in the first stage results from weighing the anticipated gain in information with effective treatment; the objective is to maximize the expected number of successes in the entire trial. This is in contrast to randomized controlled trials with the restricted objective of obtaining information concerning treatment differences. We allow the length of the first stage to be arbitrary and fixed in advance, or optimized as a function of prior information and the ‘patient horizon’. We can regard this patient horizon as either the number of patients in the trial or the number who have the condition under treatment. We consider two forms of prior information: (i) both success probabilities known but the better of the two treatments is unknown, and (ii) one success probability known whereas the other has an arbitrary distribution. In many instances of the latter case the optimal first stage size is of the order of the square root of the patient horizon.
An application of bayesian analysis to medical follow‐up data
Authors: Achcar Jorge A. , Brookmeyer Ron , Hunter William G. 
Published: April 2007

AbstractPosterior distributions can provide effective summaries of the main conclusions of medical follow‐up studies. In this article, we use Bayesian methods for the analysis of survival data. We describe posterior distributions for various parameters of clinical interest in the presence of arbitrary right censorship. Non‐informative reference priors result from transformation of a two‐parameter Weibull model into a location‐scale family. We suggest an approach for checking adequacy. For illustration, we apply the methods to a well‐known acute leukemia data set.
Analysis of the clinical utility of a predictive chemosensitivity assay
Authors: Korn Edward L. , Sondak Vernon K. , Bertelsen Carl A. , Kern David H. 
Published: April 2007

AbstractWe present an elementary statistical analysis for quantifying the clinical utility of a predictive chemosensitivity assay based on retrospective data. An assay predictive of patient response could possibly improve response rates and reduce morbidity by individualizing chemotherapy for each patient. An analysis of retrospective data can suggest appropriate patient populations and sample sizes for study in prospective trials using the chemosensitivity assay. We provide an example with data from a clonogenic assay collected on melanoma patients.