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PubMed2002

Comparing results of large clinical trials to those of meta-analyses.

We consider methods for assessing agreement or disagreement between the results of a meta-analysis of small studies addressing a clinical question and the result of a large clinical trial (LCT) addressing the same clinical question. We recommend basing conclusions about agreement upon the difference between the two results (relative risk, log-odds ratio or similar summary statistic), in the light of the estimated standard error of that difference. To estimate the standard error of the meta-analytic result we recommend a random effects analysis, and where a between-studies variance component is found, that component of variance should be used twice: once in the estimated standard error for the meta-analytic result and again in the standard error of the LCT result (augmenting the internal standard error of that statistic). Such broadening of the standard error reduces the appearance of disagreement. We also offer a critique of a different published approach, which is based on consistency of findings of statistical significance, a matter of how the two results regard zero, which is a poor measure of how closely they agree with each other.

Clinical Trials as Topic↗
PubMed2002

Single-factor repeated-measures designs: analysis and interpretation.

In this column we discussed the selection and interpretation of appropriate statistical tests for single-factor within-subjects/ repeated-measures designs and provided an example from the literature. The parametric tests that we discussed were the t test for paired or correlated samples and the single-factor repeated-measures ANOVA. We also mentioned four nonparametric tests to be used in single-factor within-subjects/repeated-measures designs, but they are relatively rare in the literature. The Compton et al. (2001) article did not provide effect size measures, but they could be computed from the means and standard deviations. Remember that a statistically significant t or ANOVA (even ifp < .001) does not mean that there was a large effect, especially if the sample was large. In the Compton example, the sample was quite small (N = 14), and the findings do reflect a large effect size.

Adolescent↗
PubMed2006

Extension of the rank sum test for clustered data: two-group comparisons with group membership defined at the subunit level.

The Wilcoxon rank sum test is widely used for two-group comparisons for nonnormal data. An assumption of this test is independence of sampling units both between and within groups. In ophthalmology, data are often collected on two eyes of an individual, which are highly correlated. In ophthalmological clinical trials, randomization is usually performed at the subject level, but the unit of analysis is the eye. If the eye is used as the unit of analysis, then a modification to the usual Wilcoxon rank sum variance formula must be made to account for the within-cluster dependence. For some clustered data designs, where the unit of analysis is the subunit, group membership may be defined at the subunit level. For example, in some randomized ophthalmologic clinical trials, different treatments may be applied to fellow eyes of some patients, while the same treatment may be applied to fellow eyes of other patients. In general, binary eye-specific covariates may be present (scored as exposed or unexposed) and one wishes to compare nonnormally distributed outcomes between exposed and unexposed eyes using the Wilcoxon rank sum test while accounting for the clustering. In this article, we present a corrected variance formula for the Wilcoxon rank sum statistic in the setting of eye (subunit)-specific covariates. We apply it to compare ocular itching scores in ocular allergy patients between eyes treated with active versus placebo eye drops, where some patients receive the same eye drop in both eyes, while other patients receive different eye drops in fellow eyes. We also present comparisons between the clustered Wilcoxon test and each of the signed rank tests and mixed model approaches and show dramatic differences in power in favor of the clustered Wilcoxon test for some designs.

Biometry↗
PubMed2001

On the probability of cost-effectiveness using data from randomized clinical trials.

BACKGROUND: Acceptability curves have been proposed for quantifying the probability that a treatment under investigation in a clinical trial is cost-effective. Various definitions and estimation methods have been proposed. Loosely speaking, all the definitions, Bayesian or otherwise, relate to the probability that the treatment under consideration is cost-effective as a function of the value placed on a unit of effectiveness. These definitions are, in fact, expressions of the certainty with which the current evidence would lead us to believe that the treatment under consideration is cost-effective, and are dependent on the amount of evidence (i.e. sample size). METHODS: An alternative for quantifying the probability that the treatment under consideration is cost-effective, which is independent of sample size, is proposed. RESULTS: Non-parametric methods are given for point and interval estimation. In addition, these methods provide a non-parametric estimator and confidence interval for the incremental cost-effectiveness ratio. An example is provided. CONCLUSIONS: The proposed parameter for quantifying the probability that a new therapy is cost-effective is superior to the acceptability curve because it is not sample size dependent and because it can be interpreted as the proportion of patients who would benefit if given the new therapy. Non-parametric methods are used to estimate the parameter and its variance, providing the appropriate confidence intervals and test of hypothesis.

Cost-Benefit Analysis↗
PubMed2003

Are our data symmetric?

Skewness indicates a lack of symmetry in a distribution. Knowing the symmetry of the underlying data is essential for parametric analysis, fitting distributions or doing transformations to the data. The coefficient of skewness is the commonly used measure to identify a lack of symmetry in the underlying data, although graphical procedures can also be effective. We discuss three different methods to assess skewness: traditional coefficient of skewness index, skewness index based on the L-moments discussed by Hosking and the asymptotic test of symmetry developed by Randles et al. With this work, we provide easy-to-implement S-PLUS functions as well as discuss the advantages and shortcomings of each technique.

Biometry↗
PubMed1990

Health care indicators.

Contained in this regular feature of the journal is a section on each of the following four topics: community hospital statistics; employment, hours, and earnings in the private health sector; health care prices; and national economic indicators.

Economics, Hospital↗
PubMed2003

A cautionary note on exact unconditional inference for a difference between two independent binomial proportions.

Fisher's exact test for comparing response proportions in a randomized experiment can be overly conservative when the group sizes are small or when the response proportions are close to zero or one. This is primarily because the null distribution of the test statistic becomes too discrete, a partial consequence of the inference being conditional on the total number of responders. Accordingly, exact unconditional procedures have gained in popularity, on the premise that power will increase because the null distribution of the test statistic will presumably be less discrete. However, we caution researchers that a poor choice of test statistic for exact unconditional inference can actually result in a substantially less powerful analysis than Fisher's conditional test. To illustrate, we study a real example and provide exact test size and power results for several competing tests, for both balanced and unbalanced designs. Our results reveal that Fisher's test generally outperforms exact unconditional tests based on using as the test statistic either the observed difference in proportions, or the observed difference divided by its estimated standard error under the alternative hypothesis, the latter for unbalanced designs only. On the other hand, the exact unconditional test based on the observed difference divided by its estimated standard error under the null hypothesis (score statistic) outperforms Fisher's test, and is recommended. Boschloo's test, in which the p-value from Fisher's test is used as the test statistic in an exact unconditional test, is uniformly more powerful than Fisher's test, and is also recommended.

Humans↗
PubMed2003

Statistics in three biomedical journals.

In this paper we analyze the use of statistics and associated problems, in three Czech biological journals in the year 2000. We investigated 23 articles Folia Biologica, 60 articles in Folia Microbiologica, and 88 articles in Physiological Research. The highest frequency of publications with statistical content have used descriptive statistics and t-test. The most usual mistake concerns the absence of reference about the used statistical software and insufficient description of the data. We have compared our results with the results of similar studies in some other medical journals. The use of important statistical methods is comparable with those used in most medical journals, the proportion of articles, in which the applied method is described insufficiently is moderately low.

Czech Republic↗
PubMed1987

The reporting of statistical techniques in otolaryngology journals.

The domain of this study is the reporting of statistical analyses in the otolaryngology literature during 1983 and 1984. Fewer than ten basic statistical procedures accounted for more than 90% of the statistical techniques reported. Implications for authors, journals, and educators are discussed. We offer suggestions for imparting statistical skills that may be helpful in curriculum design, residency training, and continuing medical education planning.

Humans↗
PubMed1992

Statistical techniques in ophthalmic journals.

Over the years, the use of statistics to evaluate experimental data in ophthalmology has increased. The present study sought to assess the frequency and types of statistical techniques used in ophthalmic journals. We reviewed 974 original articles from the Archives for 1970, 1980, and 1990; the American Journal of Ophthalmology for 1990; and Ophthalmology for 1990. Of the 592 articles reviewed for 1990, 391 (66.0%) contained statistics, with measures of central tendency most commonly used (385 articles [65.0%]), followed by dispersion (298 [50.3%]), t test (120 [20.3%]), and contingency tables (98 [16.6%]). A reader familiar with 10 statistical techniques would have "statistical accessibility" to 526 (88.9%) of 1990 articles. A statistically significant difference was found in the percentage of articles containing statistical methods among the journals (P = .0003; Archives, 75.3%; Ophthalmology, 66.8%; and American Journal of Ophthalmology, 55.2%).

Animals↗
PubMed2003

[Ethical problems in randomized clinical studies from the aspect of statistics. Part II: when should patient randomization be stopped of modified?].

The ethical responsibility to the randomized study participants demands that the results be monitored during the course of the trial. The interim evaluation of the trial results may lead to the premature stopping. However, the repeated statistical testing inflates the probability of false positive error. Hence statistical adjustments are necessary. The probabilistic rules for the random allocation of patients may be changed during the course of the trial according to the observed responses.

Humans↗
PubMed1991

Meta-analysis: the fashion of summing-up evidence. Part I. Rationale and conduct.

Meta-analysis is the process of formally combining the quantitative results of separate studies in order to increase the statistical precession of estimated effects. It has become fashionable when individual studies fail to yield conclusive results. A recent update of a meta-analysis (overview) for treatments of patients with early breast cancer motivated this commentary to discuss the rationale, principles of conduct, statistical methods, and graphical display for summing up results. In part II we will approach the issue of interpretation and use of overview data.

Bayes Theorem↗
PubMed1987

Statistical techniques reported in pathology journals during 1983-1985. Implications for pathology educators.

The increasingly scientific basis of medicine challenges pathology educators to incorporate quantitative skills into a very compressed curriculum. One strategy is to focus training on the statistical techniques pathologists will most commonly encounter in their literature. We identified the reporting of statistical techniques in nearly 5200 original articles published during 1983-1985 in 16 journals important to pathology. Our results suggest that a reader familiar with 12 fundamental statistical concepts can evaluate knowledgeably over 95% of the quantitative findings reported in these journals. With the exception of survival analysis and pharmacologic modeling, these techniques are typically encountered in many introductory statistical texts. In numerous articles, failure to identify the statistical methodology used made it impossible to identify the analytic procedures used and, hence, judge the scientific validity of results.

Curriculum↗
PubMed1993

The use of external monitoring committees in clinical trials of the National Institute of Allergy and Infectious Diseases.

Randomized clinical trials are being conducted and/or sponsored by all scientific divisions of the National Institute of Allergy and Infectious Diseases (NIAID). External committees to review the progress of ongoing trials and to make recommendations to the Institute concerning continuation or termination are an integral part of many of these trials. These committees have evolved considerably from the ad hoc committees, called together when a need arose, which were used beginning in the mid 1970s. Currently, there are many monitoring committees operating for NIAID-sponsored trials. They function in a variety of ways, based partially on historical precedent and partially on the specialized requirements of the particular trial; there is no 'standard operating procedure' for the Institute, or even for divisions within the Institute. One of the major issues faced in establishing the data and safety monitoring board for AIDS treatment trials was access to the meetings of this board and to the reports of interim data that the board reviewed. After much discussion, procedures were established that restrict such access to a very limited group of programme and statistical centre staff. These procedures, while remaining controversial, appear necessary to ensure confidentiality and the integrity of the clinical trials process.

Acquired Immunodeficiency Syndrome↗
PubMed2002

On the issue of 'multiple' first failures in competing risks analysis.

In the classical competing risks framework, a subject may only fail from one of several distinct causes. However, in the context of cancer clinical trials where information on first relapse is usually of interest, there could be occasions when 'multiple' first recurrences are identified at a particular follow-up. In this instance, the competing risks methodology cannot be implemented without first tackling the issue of 'tied' first failure. When the tied events were substantial, Arriagada et al. regarded each competing failure separately, and combined the 'simultaneous' failures into a single category for analysis. This paper describes two other methods of accounting for 'multiple' failures. First, the ties were dealt with by applying a weighting factor which was equal to the reciprocal of the number of ties. We also considered 'jittering' which randomly adds or subtracts a small number to each 'tied' event time to randomly break the tie. As illustrated using the data obtained from a randomized trial of patients with operable osteosarcoma, the estimates based on Arriagada's approach have larger standard errors. Estimates from the other alternative methods were similar. Multiple jittering has the advantage of wide applicability in any situation of tied survival times. However, it takes a longer computer running time, especially when the number of replicates is large. The weighted Cox approach is the method of choice where statistical software allows its implementation without extra programming effort.

Antineoplastic Agents↗
PubMed2004

Five-year change in statistical designs of phase II trials published in leading cancer journals.

This study compares the evolution in statistical design reporting for phase II cancer clinical trials published in the six following leading journals: American Journal of Clinical Oncology, Annals of Oncology, British Journal of Cancer, Cancer, European Journal of Cancer and Journal of Clinical Oncology. Only articles where tumour response was considered as the primary endpoint were selected. A total of 393 phase II trials published in 1995 (n=185) and 2000 (n=208) were reviewed. Neither sample size nor design parameters were specified in 157 (85%) and 113 (46%) papers in 1995 and 2000, respectively. 28 (15%) and 95 (46%) papers included at least some information on the statistical designs used: Gehan (4.3% and 3.3%), Fleming (2.2% and 4.3%), and Simon (2.7% and 11.0%). Ad hoc, non-referenced methods were used in 5.9% and 27.3% articles in 1995 and 2000, respectively. Although there is an increase in the mention of at least some statistical design parameters in phase II cancer clinical trials over a 5-year period in these selected cancer journals, the use of referenced methods is still short or often inadequate.

Clinical Trials, Phase II as Topic↗