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PubMed2006

Combining dependent tests to compare the diagnostic accuracies--a non-parametric approach.

In this paper, we propose a non-parametric approach for comparing diagnostic accuracies in multi-reader receiver operating characteristic (ROC) studies. The approach constructs a test from each reader by extending the conventional non-parametric method and then combines all the individual test statistics to draw an overall conclusion on the relative accuracies of different diagnostic tests. The method can handle both continuous and ordinal data. Compared to the existing non-parametric methods, the method is robust and effectively deals with the possible heterogeneity among readers. It can also be applied to the analysis of correlated ROC studies. The method is applied to a real example and its finite sample performance is examined through simulation studies.

Analysis of Variance↗
PubMed2003

Nonparametric quantile estimation with correlated failure time data.

In biomedical studies, correlated failure time data arise often. Although point and confidence interval estimation for quantiles with independent censored failure time data have been extensively studied, estimation for quantiles with correlated failure time data has not been developed. In this article, we propose a nonparametric estimation method for quantiles with correlated failure time data. We derive the asymptotic properties of the quantile estimator and propose confidence interval estimators based on the bootstrap and kernel smoothing methods. Simulation studies are carried out to investigate the finite sample properties of the proposed estimators. Finally, we illustrate the proposed method with a data set from a study of patients with otitis media.

Child, Preschool↗
PubMed2006

Response-adaptive randomization for clinical trials with continuous outcomes.

We provide an explicit asymptotic method to evaluate the performance of different response-adaptive randomization procedures in clinical trials with continuous outcomes. We use this method to investigate four different response-adaptive randomization procedures. Their performance, especially in power and treatment assignment skewing to the better treatment, is thoroughly evaluated theoretically. These results are then verified by simulation. Our analysis concludes that the doubly adaptive biased coin design procedure targeting optimal allocation is the best one for practical use. We also consider the effect of delay in responses and nonstandard responses, for example, Cauchy distributed response. We illustrate our procedure by redesigning a real clinical trial.

Biometry↗
PubMed1989

Antiplatelet or anticoagulant therapy after coronary artery bypass surgery. A meta-analysis of clinical trials.

PURPOSE: To determine the efficacy of antiplatelet or anti-coagulant therapy in preventing graft occlusions after coronary artery bypass surgery. DATA IDENTIFICATION: Studies published from 1966 to 1988 were identified through a computerized search using MEDLINE, by searching the bibliographies of all identified articles, and by consulting with the cardiologists and cardiothoracic surgeons in the Veterans Administration Cooperative Study Group on Antiplatelet Therapy After Coronary Artery Bypass Surgery. STUDY SELECTION: All studies selected were randomized, controlled clinical trials comparing at least one active drug with a placebo or nonplacebo control group. DATA EXTRACTION: Key data were extracted from each article, including the percentage of patients in each treatment group with one or more grafts occluded, the percentage of patients with completed postoperative catheterizations, timing of postoperative catheterization, and timing of start of treatment. These data were easily obtained from each article and did not require multiple observers. RESULTS OF DATA ANALYSIS: All studies had positive treatment-effect sizes in favor of active treatment, although some studies did not achieve statistical significance. A meta-analysis combining all treatment effects clearly shows that active treatment is beneficial (overall effect size = 0.30; CI, 0.21 to 0.38). Efficacy improves with early initiation of treatment. CONCLUSIONS: Early initiation of antiplatelet or anticoagulant drugs reduces the incidence of graft occlusions after coronary artery bypass surgery.

Anticoagulants↗
PubMed1991

Crossover trials, degrees of freedom, the carryover problem and its dual.

The problem of carryover in crossover trials has received a great deal of attention in the statistical literature. Carryover is just one form of period by treatment interaction; yet a parallel problem of patient by treatment interaction, which may be regarded as dual to that of carryover, has received little attention. We suggest that the phenomenon of patient by treatment interaction requires a repeated measures approach to the analysis of crossover trials. A simple solution using predefined contrasts is presented and illustrated by example.

Analysis of Variance↗
PubMed1996

Corticosteroid injections for lateral epicondylitis: a systematic overview.

BACKGROUND: Lateral epicondylitis (tennis elbow) is a common complaint, for which corticosteroid injections are a frequently applied therapy. However, there were no up-to-date reviews available that systematically addressed the effectiveness and adverse effects, including questions concerning optimal timing of injections and composition of the injection fluid. AIM: The aim of the study was to assess the effectiveness of corticosteroid injections in the treatment of lateral epicondylitis (tennis elbow) by systematic review of the available randomized clinical trials. DATA SOURCES: The data sources used were randomized clinical trials identified by literature searches of the MedLine (1966-1994) and Embase (Exerpta Medica) (1980-1994) databases for the keywords epicondylitis, tendinitis and elbow, injection. References given in relevant publications were further examined. STUDY SELECTION: The criteria for selecting studies were as follows: randomized clinical trials (treatment allocation in random or alternate order); one of the treatments to include one or more corticosteroid injections (additional interventions were allowed); participants suffering from lateral epicondylitis; and publication in English, German or Dutch. Abstracts and unpublished studies were not included. DATA SYNTHESIS: Methodological quality was assessed by means of a standardized criteria list (range 1-100 points). The extracted outcomes were the general conclusion drawn by the authors of the reports on the trials, and the success rates at the various follow-up points as (re)calculated by us. The success rates were subsequently graphically displayed and statistically pooled. Separate stratified analyses were conducted according to a predetermined analysis plan. RESULTS: Twelve randomized clinical trials were identified. The median methodological score was 40 points, indicating an overall poor to moderate quality. The pooled analysis indicated short-term effectiveness (2-6 weeks): pooled odds ratio (OR) = 0.15 [95% confidence interval (CI) 0.10-0.23], chi 2 [degrees of freedom (df = 5) = 13.3], indicating statistical heterogeneity. At longer term follow-up, no difference could be detected. The studies of better methodological quality indicated more favourable results than those of lesser methodological quality. The most suitable corticosteroid to use as well as dosage, injection interval and injection volume could not be derived from the various trials. CONCLUSION: The existing evidence on corticosteroid injections for the treatment of tennis elbow is not conclusive. Many trials were conducted in a secondary care setting and clearly had serious methodological flaws, and there was statistical heterogeneity among the trials. Corticosteroid injections appear to be relatively safe and seem to be effective in the short term (2-6 weeks). Although the treatment seems to be suitable for application in general practice, further trials in this setting are needed. As yet, questions regarding the optimal timing, dosage, injection technique and injection volume remain unanswered.

Adrenal Cortex Hormones↗
PubMed2002

Using imprecise probabilities to address the questions of inference and decision in randomized clinical trials.

Randomized controlled clinical trials play an important role in the development of new medical therapies. There is, however, an ethical issue surrounding the use of randomized treatment allocation when the patient is suffering from a life threatening condition and requires immediate treatment. Such patients can only benefit from the treatment they actually receive and not from the alternative therapy, even if it ultimately proves to be superior. We discuss a novel new way to analyse data from such clinical trials based on the use of the recently developed theory of imprecise probabilities. This work draws an explicit distinction between the related but nevertheless distinct questions of inference and decision in clinical trials. The traditional question of scientific interest asks 'Which treatment offers the greater chance of success?' and is the primary reason for conducting the clinical trial. The question of decision concerns the welfare of the patients in the clinical trial, asking whether the accumulated evidence favours one treatment over the other to such an extent that the next patient should decline randomization and instead express a preference for one treatment. Consideration of the decision question within the framework of imprecise probabilities leads to a mathematical definition of equipoise and a method for governing the randomization protocol of a clinical trial. This paper describes in detail the protocol for the conduct of clinical trials based on this new method of analysis, which is illustrated in a retrospective analysis of data from a clinical trial comparing the anti-emetic drugs ondansetron and droperidol in the treatment of postoperative nausea and vomiting. The proposed methodology is compared quantitatively using computer simulation studies with conventional clinical trial designs and is shown to maintain high statistical power with reduced sample sizes, at the expense of a high type I error rate that we argue is irrelevant in some specific circumstances. Particular emphasis is placed on describing the type of medical conditions and treatment comparisons where the new methodology is expected to provide the greatest benefit.

Antiemetics↗
PubMed1977

Finding the missing information in cancer statistics.

The current cancer literature is imprecise and confusing. This hampers the ability to draw meaningful conclusions regarding diagnosis and treatment. It is suggested that all future reporting of statistics contain the following features: (1) discussion of case selection criteria; (2) use of TNM system for case classification; (3) listing of minimal treatment details; (4) explanation for length of follow-up used; (5) standardized terms for evaluation (relating these to individual TNM classification); and (6) listing of all failures by standardized terms. It is proposed that editors of journals and organizers of meetings reject all papers that do not meet these criteria.

Bibliographies as Topic↗
PubMed2006

Quality of scientific articles.

The paper discusses the difficulties in judging the quality of scientific manuscripts and describes some common pitfalls that should be avoided when preparing a paper for submission to a peer-reviewed journal. Peer review is an imperfect system, with less than optimal reliability and uncertain validity. However, as it is likely that it will remain as the principal process of screening papers for publication, authors should avoid some common mistakes when preparing a report based on empirical findings of human research. Among these are: excessively long abstracts, extensive use of abbreviations, failure to report results of parsimonious data analyses, and misinterpretation of statistical associations identified in observational studies as causal. Another common problem in many manuscripts is their excessive length, which makes them more difficult to be evaluated or read by the intended readers, if published. The evaluation of papers after their publication with a view towards their inclusion in a systematic review is also discussed. The limitations of the impact factor as a criterion to judge the quality of a paper are reviewed.

Animals↗
PubMed1998

Statistical reviewing for medical journals.

This paper reviews the difficulties associated with being a statistical reviewer for a medical journal. As background, I consider first the use of statistical reviewers by medical journals, medical journals' policies on statistical peer review, and the limited evidence of its effectiveness. The assessment of a manuscript is considered under the headings of design, methods of analysis, presentation and interpretation, with many illustrative examples of the difficulties to be overcome. I emphasize the judgemental nature of many aspects. I suggest how to present and structure the reviewer's report to the editor. Finally, I consider wider issues, including the various other ways in which statisticians can interact with medical journals.

Peer Review, Research↗
PubMed2006

Statistical methods for analysing Barthel scores in trials of poststroke interventions: a review and computer simulations.

BACKGROUND AND PURPOSE: Arguments persist as to whether parametric or non-parametric methods should be used to analyse ordinal data in trials. This paper aims to assess methods used for presenting and analysing an ordinal scale, the Barthel Index, in trials of poststroke interventions. METHODS: All randomized controlled trials (RCTs) of poststroke interventions published from 1995 to 2004 in two journals (Stroke and Clinical Rehabilitation) were scrutinized for methods used to present and analyse Barthel scores. Computer simulations were used to compare the type I errors and the statistical power of different statistical methods under a range of assumed circumstances. RESULTS: One hundred and fifty-six RCTs were identified within the two journals. The central tendency of Barthel scores was measured by the median in 47 trials and by the mean in 35 trials. Non-parametric analyses of Barthel scores were conducted in 47 trials and parametric methods used in 18 trials. The results of computer simulations demonstrate that the t-test has a similar type I error rate and statistical power when compared with the rank sum test. However, when a zero final Barthel score is assigned to patients who have died, the statistical power of the t-test is much reduced. The possible maximal statistical power of dichotomization and ordinal regression is usually much lower than that of the rank sum test. CONCLUSIONS: To facilitate comparison and meta-analysis, we recommend that mean values (with standard deviations or standard errors) of Barthel scores should be routinely reported in trials of poststroke interventions. The rank sum test appears the most powerful inferential technique for detecting differences in Barthel scores.

Computer Simulation↗
PubMed1985

Some properties of the USP content-uniformity test as related to control charts and validation of solid dosage forms.

The statistical properties of the USP content-uniformity test have been investigated in detail in other reports. This note shows that control charts for the mean potency of a solid dosage form which are constructed using typical individual content-uniformity assays in conjunction with composite assay(s), show tight limits when the product has a high probability of passing the content-uniformity test. From a practical point of view, this is a strong argument in favor of the test and recommends the test as a quality control tool.

Pharmacopoeias as Topic↗
PubMed1987

The beta error and sample size determination in clinical trials in emergency medicine.

In the analysis of a clinical trial an investigator may fail to discern a statistically significant difference in outcome between control and experimental groups, when in fact one exists. Failure to demonstrate such a difference when it actually exists is known as "type II" error, and its probability of occurring is termed "beta." The purpose of our study was to determine the distribution of beta errors in negative trials in the Journal of the American College of Emergency Physicians (JACEP) (1972-1979) and Annals of Emergency Medicine (1980-1984). All negative comparative clinical trials appearing in JACEP and Annals from volume 1 (1972) to volume 13 (1984) were surveyed and were eligible for inclusion in the study. A trial was defined as negative if the investigator specifically stated that there was no significant difference in outcome between the experimental and control groups. For each negative trial the following parameters were calculated: beta error, based on the sample size used and the difference determined to be important to detect clinically; sample size required to detect a clinically meaningful difference as determined by the authors of this study; and minimum true difference that had to be detected in the trial at a beta equal to 0.20, to discern a statistically significant result. For the 13 years surveyed, we found 21 endpoints in 14 negative trials that were analyzable. Only one of the trials (7.1%) addressed the issues of beta errors and sample size determination. In the remaining 13 negative trials, the calculated beta error ranged from .60 to .97. For the endpoints analyzed, a sample size of up to 450 times larger than that used would have been required to detect a clinically important difference.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical Trials as Topic↗
PubMed1978

[Pediatric bibliometrics: II. Descriptive statistics on pediatric periodicals and papers (author's transl)].

A descriptive statistic study about journals and pediatric articles at international level is presented. Three of the main international repetories of medical bibliography, have been used as sources, collecting a total of three hundred periodical pediatric publications. A distribution of these publications by languages, places or impression, periodicity of appearance and percent of sub-specialization is made. In relation with pediatric papers, we have studied their presence in non medical scientific journals, medical but non pediatric journals and in those of the speciality, analizing the percentage of these papers in each one of them.

Pediatrics↗
PubMed1990

Evaluation of statistics teaching given to medical undergraduates.

Medical undergraduates in all United Kingdom medical schools receive statistics teaching, but attempts to establish the efficacy of this teaching have been scanty. Establishment of clear educational objectives is a prerequisite to meaningful evaluation. Most medical schools have attempted to obtain feedback from their students by administering questionnaires. Examination performance can provide very pertinent information if a finely detailed marking scheme is developed, identifying issues that are generally poorly grasped. Controlled trials may be carried out within an institution but encounter problems of contamination and low power. It should eventually be possible to develop multi-institutional evaluation methods.

Education, Medical, Undergraduate↗
PubMed2001

On tests of the overall treatment effect in meta-analysis with normally distributed responses.

For the meta-analysis of controlled clinical trials or epidemiological studies, in which the responses are at least approximately normally distributed, a refined test for the hypothesis of no overall treatment effect is proposed. The test statistic is based on a direct estimation function for the variance of the overall treatment effect estimator. As outcome measures, the absolute and the standardized difference between means are considered. In simulation studies it is shown that the proposed test keeps the prescribed significance level very well in contrast to the commonly used tests in the fixed effects and random effects model, respectively, which can become very liberal. Furthermore, just for using the proposed test it is not necessary to choose between the fixed effects and the random effects approach in advance.

Amlodipine↗
PubMed1991

On estimating efficacy from clinical trials.

We define 'biologic efficacy' as the effect of treatment for all persons who receive the therapeutic agent to which they were assigned. It measures the biologic action of treatment among compliant persons. In a randomized trial with one treatment and one placebo control, one can theoretically estimate efficacy by comparing persons who complete the treatment regimen with controls who similarly complete the control regimen. In practice, however, we make this comparison with reservation because a control protocol often presents a different challenge for compliance than does the treatment, so that the compliant subgroups are not comparable. Standard practice employs intent-to-treat comparisons in which one compares those randomized to treatment and control without reference to whether they actually received the treatment. Intent-to-treat comparisons estimate the 'programmatic effectiveness' of a treatment rather than its biologic efficacy. This paper introduces and derives the statistical properties of an alternative estimator of biologic efficacy that avoids the potential selection bias inherent in a comparison of compliant subgroups. The method applies to randomized trials with a dichotomous outcome measure, whether or not a placebo is given to the control group. The idea is to compare the compliers in the treatment group to an inferred control subgroup chosen to eliminate selection bias. The methodology was motivated by and is illustrated in the analysis of a randomized community trial of the impact of vitamin A supplementation on children's mortality.

Bias↗
PubMed2004

Hypochondriacal concerns in panic disorder and major depressive disorder: a comparison.

OBJECTIVE: To gain perspective on the relationship between hypochondriasis and panic disorder, we compared the occurrence of hypochondriasis in patients with panic disorder (N= 59) and major depressive disorder (N= 27). METHODS: Patients who participated in separate drug treatment trials were assessed at baseline and eight weeks using the Whiteley Index of Hypochondriasis. RESULTS: At baseline, the Whiteley Index score was greater for patients with panic disorder than for those with major depressive disorder. At eight weeks, a statistically significant reduction in the mean hypochondriasis score was observed in panic patients who had improved but not in major depressive patients who had improved. Modest correlations were observed between hypochondriasis and symptoms of panic and major depressive disorder, but in depressed patients, hypochondriasis was positively correlated with anxiety symptoms as well. CONCLUSION: A unique relationship appears to exist between hypochondriasis and panic disorder. The nature of this relationship and its implications for classification are discussed.

Adult↗