Biomedical subjects
Publications and source records attributed to J D Emerson.
The Israeli health care system is more advanced than the American system in its universal coverage, its financing mechanism, and in its implementation of a managed competition process. Yet, it trails American developments in management of inpatient and outpatient services and in the creative design of provider reimbursements. An MCO executive provides his observations from a trade/study mission to this Middle Eastern country.
Meta-analyses often use a random-effects model to incorporate unexplained heterogeneity of study results. Trimmed versions of meta-analytic estimators for the risk difference, adapted from procedures designed for a random-effects analysis, can resist the impact of a few anomalous studies. A simulation study compared untrimmed and trimmed versions of four meta-analytic procedures that give weighted averages of risk differences. An adaptation of Winsorized estimates of components of variance gains some resistance to anomalous studies when estimating variability. The simulations found that a modified version of the DerSimonian-Laird estimator is attractive when risk differences reveal the added variability described by a random-effects model, and that a 20 per cent trimmed, weighted version of this procedure offers resistance against the impact of highly anomalous results. Among four trimmed procedures considered, the trimmed version of the modified DerSimonian-Laird estimator offers the best performance over a wide range of simulation designs and sample sizes. None of the methods, whether trimmed or untrimmed, is uniformly preferable. A published meta-analysis of a vaccination against TB provides data that serve to illustrate differences among the eight procedures.
Medical research commonly relies on the combination of 2 x 2 tables of counted data for making inferences about treatment effects or about the causes of disease. This article reviews point estimation and interval estimation for a common odds ratio. Traditional methods for providing these estimates face special challenges, and sometimes break down, when the data are sparse. Recent research provides practical alternatives to the traditional methods, and uses new computer algorithms to make them readily available in microcomputer software packages. This article illustrates and compares the various methods and offers recommendations for using the newer methods when analysing data sets of moderate size.
Meta-analytic investigations sometimes use assessments of research quality according to a formal protocol as a tool for improving research synthesis. We asked whether a particular quality scoring system could have a direct use in adjusting the summary estimates of a treatment difference. In an empirical study of the relation of quality scores to treatment differences in published meta-analyses of 7 groups of controlled randomized clinical trials comprising 107 primary studies, we found no relation between treatment difference and overall quality score. We also found no relation between quality score and variation in treatment difference. The level of quality scores has increased at a rate of 9% per decade for three decades, averaging 0.51 on a scale of 0 to 1 for the 1980s, and leaving much room for improvement. Nevertheless, attention to quality of studies by editors, reviewers, and authors may be raising both the level of research done and quality of the reports.
Medical researchers and policy makers face decisions that require a choice from among two or more alternatives. Whereas traditional hypothesis tests cannot always serve the needs of the practitioner who needs to make a decision, a problem formulation that assigns losses to various incorrect decisions offers several advantages. With three possible decisions this approach offers a precise representation of the pragmatic and explanatory views of decision making. It enables the investigator to incorporate in the problem specification his attitudes about the seriousness of various errors by guiding him, before he sees the data, to a choice of asymmetric tail probabilities. It also suggests a reformulation of the P-value that can accommodate some of the difficulties practitioners face.
Medical students and doctors need training in biostatistics. The use of analytic statistics in a leading general medical journal is reported. Of 760 consecutive research and review articles, 42% use statistical methods beyond elementary descriptive statistics. Critical reading of the medical literature requires an understanding of many statistical methods. The frequency of use of such methods may help identify those which should receive greater attention in instructional programmes within the medical curriculum. Based on the frequencies and our understanding of the importance of broad statistical concepts, recommendations are developed for the basic course in biostatistics. The integration of several more advanced statistics modules into clinical training is also suggested. The use is recommended of clinically oriented textbooks in biostatistics and current journal articles to help make instruction in statistics more relevant for preclinical students, and to help clinicians appreciate the applications of statistics to their work.
Biological and medical investigations often use ordered categorical data. When two groups are to be compared and the data for the groups fall in three or more ordered categories, the Wilcoxon-Mann-Whitney (WMW) test uses information in the ordering to give a test that is usually powerful against shift alternatives. However, such applications of WMW often involve distributions for which extensive ties play an important role. Newly available computer programs for performing exact tests give deeper insights into the characteristics of the exact WMW distributions and the suitability of normal approximations. We offer practical advice, based on experience with published biomedical data sets and on numerical studies of hypothetical ordered tables, for the use of WMW and its normal approximations.
Clinical investigations often involve data in the form of ordered categories--e.g., "worse," "unchanged," "improved," "much improved." Comparison of two groups when the data are of this kind should not be done by the chi-square test, which wastes information and is insensitive in this context. The Wilcoxon-Mann-Whitney test provides a proper analysis. Alternatively, scores may be assigned to the categories in order, and the t-test applied. We demonstrate both approaches here. Sometimes data in ordered categories are reduced to a two-by-two table by the collapsing of the high categories into one category and the low categories into another. This practice is inefficient; moreover, it entails avoidable subjectivity in the choice of the cutting point that defines the two super-categories. The Wilcoxon-Mann-Whitney procedure (or the t-test with use of ordered scores) is preferable. A survey of research articles in Volume 306 of the New England Journal of Medicine shows many instances of ordered-category data (about 20 per cent of the articles had such data) and no instance of analysis by the preferred methods presented here. We suggest that investigators who are unfamiliar with these methods should seek the assistance of a professional statistician when they must deal with such data.
Readers need information about the design and analysis of a clinical trial to evaluate and interpret its findings. We reviewed 84 therapeutic trials appearing in six general surgical journals from July 1981 through June 1982 and assessed the reporting of 11 important aspects of design and analysis. Overall, 59% of the 11 items were clearly reported, 5% were ambiguously discussed, and 36% were not reported. The frequency of reporting in general surgical journals is thus similar to the 56% found by others for four general medical journals. Reporting was best for random allocation (89%), loss to follow-up (86%), and statistical analyses (85%). Reporting was most deficient for the method used to generate the treatment assignment (27%) and for the power of the investigation to detect treatment differences (5%). We recommend that clinical journals provide a list of important items to be included in reports on clinical trials.
A sorting of the statistical methods used by authors of the 760 research and review articles in Volumes 298 to 301 of The New England Journal of Medicine indicates that a reader who is conversant with descriptive statistics (percentages, means, and standard deviations) has statistical access to 58 per cent of the articles. Understanding t-tests increases this access to 67 per cent. The addition of contingency tables gives statistical access to 73 per cent of the articles. Familiarity with each additional statistical method gradually increases the percentage of accessible articles. Original Articles use statistical techniques more extensively than other articles in the Journal. Research studies based on a longitudinal design make heavier use of statistics than do those using a cross-sectional design. The tabulations in this study should aid clinicians and medical investigators who are planning their continuing education in statistical methods, and faculty who design or teach courses in quantitative methods for medical and health professionals.
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