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Results for “Statistical power analysis”

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PubMed2005

Factors affecting statistical power in the detection of genetic association.

The mapping of disease genes to specific loci has received a great deal of attention in the last decade, and many advances in therapeutics have resulted. Here we review family-based and population-based methods for association analysis. We define the factors that determine statistical power and show how study design and analysis should be designed to maximize the probability of localizing disease genes.

Data Interpretation, Statistical↗
PubMedDate not supplied

A comparison of bivariate and univariate QTL mapping in livestock populations.

This study presents a multivariate, variance component-based QTL mapping model implemented via restricted maximum likelihood (REML). The method was applied to investigate bivariate and univariate QTL mapping analyses, using simulated data. Specifically, we report results on the statistical power to detect a QTL and on the precision of parameter estimates using univariate and bivariate approaches. The model and methodology were also applied to study the effectiveness of partitioning the overall genetic correlation between two traits into a component due to many genes of small effect, and one due to the QTL. It is shown that when the QTL has a pleiotropic effect on two traits, a bivariate analysis leads to a higher statistical power of detecting the QTL and to a more precise estimate of the QTL's map position, in particular in the case when the QTL has a small effect on the trait. The increase in power is most marked in cases where the contributions of the QTL and of the polygenic components to the genetic correlation have opposite signs. The bivariate REML analysis can successfully partition the two components contributing to the genetic correlation between traits.

Animals↗
PubMed2004

Genome scan meta-analysis for hypertension.

BACKGROUND: Genome scans for hypertension have yielded inconsistent results. The non-replication of significant or suggestive linkage might be due to lack of power of individual studies. Here, we conducted a genome scan meta-analysis for hypertension in an attempt to increase statistical power and to enhance evidence of linkage. METHODS: A newly developed Genome Search Meta-analysis (GSMA) method was applied to pool the results obtained from six scans reported in five papers. RESULTS: Our analysis did not find any regions with genome-wide significant linkage to hypertension. We did identify several regions with suggestive linkage, including 2p, 5q, 6q, 8p, 9p, 9q, and 11q. CONCLUSIONS: It seems that no region has a uniformly large impact on hypertension and that susceptibility genes for hypertension may be very difficult to detect.

Blood Pressure↗
PubMed2002

Nutritional papers in ICU patients: what lies between the lines?

The abundance of literature related to nutritional support reflects its recently recognised role in preventing metabolic complications and gut dysfunction during critical illness. However, some published studies lack relevance to critically ill patients, as a result of the selection of subjects and outcome variables, or flaws in the study design, as well as in the type, composition, timing, route of administration and amount of nutritional support given. This review will highlight these confounding factors by describing two imaginary (but typical) clinical trials and by analysing some studies published. The point at issue is that basic quality requirements, such as the formulation of a prospective hypothesis and the delineation of the effects of the reference treatment, are often lacking in many studies published. Data analysis was often found to be biased by the absence of statistical power calculation and intention-to-treat analysis. Globally, studies designed to assess the effects of nutritional support on the outcome of critically ill patients, rarely fulfil basic quality requirements and should therefore be interpreted cautiously. We suggest simple strategies or study design that will allow important questions to be answered by future clinical trials.

Clinical Trials as Topic↗
PubMed1992

Can small-area analysis detect variation in surgery rates? The power of small-area variation analysis.

A variety of statistical methods can be used in small-area analysis to test whether there is more variation than would be expected by chance alone. However, the power of these methods to detect existing variation has never been studied. The authors used data regarding back surgery in Washington State to suggest several types of variation that might exist (alternative hypotheses), and then used computer simulation to determine the power, or the probability of detecting this variation. The chi-square test had the highest power of all methods considered against most alternative hypotheses. Power is higher if there are no multiple admissions, rates are higher, and counties have larger or similar population size. Problems of accounting for multiple admissions, adjustment for age and sex, choosing the optimum size of small areas, and detection of outliers also are discussed.

Age Factors↗
PubMed2001

[Analysis of the medico-economic literature comparing primary angioplasty and thrombolysis in the management of acute myocardial infarction].

OBJECTIVE: To assess the generalizability of the medico-economic analysis comparing primary coronary angioplasty and thrombolytic therapy for acute myocardial infarction. METHOD: A systematic analysis of published studies was performed by two independent reviewers, in accordance with guidelines promulgated by health economic experts. RESULTS: Eleven articles, which concerned seven studies, were selected. Respectively, four evaluations were carried out in U.S. and three other in European countries (France, Netherland and Austria). There were three randomized trials, two observational studies and two decision trees. The costs were respectively ranged 2042 to 83,708 1999 US dollars for thrombolytic therapy and 3289 to 83,477 1999 US dollars for angioplasty. In two randomized trials and one decisional tree, the primary coronary angioplasty was both more effective and less costly than the thrombolysis therapy. One observational study concluded that thrombolytic therapy was less costly than primary angioplasty despite comparable effectiveness. Two analysis could not conclude of a difference between the alternatives, because of lack of statistical power. DISCUSSION: Published medico-economic analysis remain of a little interest for the French health care system because of lack of transparency in presentation of results. The dominance of the primary angioplasty was sensitive to time required for patient's transfer (ideally less than an hour), to the presence of redundant laboratories in an area and to the presence of an experienced staff for 24 h a day.

Angioplasty↗
PubMed2002

[Meta-analysis and evidence based medicine].

Meta-analysis is a statistical method for combining the results of available research studies to increase statistical power. The steps of meta-analysis are identification of question, search and selection of trials and analysis. Evidence based medicine (EBM) is integrating individual clinical expertise with the best available external clinical evidence from systematic research. The practice of EBM consists of formulated clinical question, systematic review, critical appraisal, application for patients and performance review. We must notice the results of meta-analysis and evidence are keeping up to date. We should use them with critical appraisal skill and should not criticize without good understanding.

Evidence-Based Medicine↗
PubMed1987

Low power argon laser trabeculoplasty.

Sixty-seven consecutive argon laser trabeculoplasties to as many patients were retrospectively followed-up for 3 to 12 (mean 7) months. The laser power used was substantially lower than originally proposed by Wise & Witter (1979) ranging from 100 mW to 500 mW. Factors influencing the outcome of low power trabebuloplasty were evaluated. The statistical analysis of the data was performed using multiple regression analysis, analysis of variance, t-test and chi 2-test. The mean success rate remained relatively low (33%). In the high power capsular glaucoma group it was 50%.

Aged↗
PubMed2006

IBZM tool: a fully automated expert system for the evaluation of IBZM SPECT studies.

PURPOSE: Visual reading of [(123)I]IBZM SPECT scans depends on the experience of the interpreter. Therefore, semi-quantification of striatal IBZM uptake is commonly considered mandatory. However, semi-quantification is time consuming and prone to error, particularly if the volumes of interest (VOIs) are positioned manually. Therefore, the present paper proposes a new software tool ("IBZM tool") for fully automated and standardised processing, evaluation and documentation of [(123)I]IBZM SPECT scans. METHODS: The IBZM tool is an easy-to-use SPM toolbox. It includes automated procedures for realignment and summation of multiple frames (motion correction), stereotactic normalisation, scaling, VOI analysis of striatum-to-reference ratio R, classification of R and standardised display. In order to evaluate the tool, which was developed at the University of Hamburg, the tool was transferred to the University of Hannover. There it was applied to 27 well-documented subjects: eight patients with multi-system atrophy (MSA), 12 patients with Parkinson's disease (PD) and seven controls. The IBZM tool was compared with manual VOI analysis. RESULTS: The sensitivity and specificity of the IBZM tool for the differentiation of the MSA subjects from the controls were 100% and 86%, respectively. The IBZM tool provided improved statistical power compared with manual VOI analysis. CONCLUSION: The IBZM tool is an expert system for the detection of reduced striatal D(2) availability on [(123)I]IBZM SPECT scans. The standardised documentation supports visual and semi-quantitative evaluation, and it is useful for presenting the findings to the referring physician. The IBZM tool has the potential for widespread use, since it appears to be fairly independent of the performance characteristics of the particular SPECT system used. The tool is available free of charge.

Adult↗
PubMed2005

Size of treatment effects and their importance to clinical research and practice.

In randomized clinical trails (RCTs), effect sizes seen in earlier studies guide both the choice of the effect size that sets the appropriate threshold of clinical significance and the rationale to believe that the true effect size is above that threshold worth pursuing in an RCT. That threshold is used to determine the necessary sample size for the proposed RCT. Once the RCT is done, the data generated are used to estimate the true effect size and its confidence interval. Clinical significance is assessed by comparing the true effect size to the threshold effect size. In subsequent meta-analysis, this effect size is combined with others, ultimately to determine whether treatment (T) is clinically significantly better than control (C). Thus, effect sizes play an important role both in designing RCTs and in interpreting their results; but specifically which effect size? We review the principles of statistical significance, power, and meta-analysis, and commonly used effect sizes. The commonly used effect sizes are limited in conveying clinical significance. We recommend three equivalent effect sizes: number needed to treat, area under the receiver operating characteristic curve comparing T and C responses, and success rate difference, chosen specifically to convey clinical significance.

Area Under Curve↗
PubMed2003

Meta-analyses of cluster randomization trials. Power considerations.

A commonly cited purpose for conducting a meta-analysis of randomized trials is to increase the statistical power for detecting the effect of an intervention on a specified set of endpoints. At the same time, it also has been noted by several authors that many large-scale cluster randomization trials have not had the power to detect small or even moderate effect sizes. The loss of efficiency associated with cluster randomization relative to individual randomization, and the frequent failure of investigators to take this loss of efficiency into account at the planning stage of a trial, undoubtedly contributes to this problem. In this article, the authors present an approach that may be used to estimate the power of a planned meta-analysis that includes trials that are cluster randomized. Two examples are presented.

Cluster Analysis↗
PubMed1992

The power of statistical studies in consultation-liaison psychiatry.

Several authors recently have proclaimed the need for empirically based research articles in consultation-liaison psychiatry. The authors report that although the proportion of empirically based studies published in Psychosomatics increased 148% from 1979 to 1989, the power of statistical analyses and the deleterious effect of multiple tests were often neglected. A power analysis of empirical studies published in the 1989 volume year of Psychosomatics is reported, showing statistical power to be low for all but the most robust of effect sizes.

Female↗
PubMed1981

Standardization vs. normalization in the power spectral analysis of the EEG signal.

Data from power analysis of the human EEG were processed statistically, and an area within the power spectrum was identified, limited by the abscissa and by an exponential curve, the parameters of which could be defined by a moving linear regression after logarithmic transform of the spectral data. The EEG signal of normal subjects and epileptics with borderline EEG tracings was studied before and after administration of neuroactive compounds. The exponential curve was found to be negative in all subjects; its parameters were symmetrical and were not modified by the drugs administered, though these were active on the spectral profile. The area limited by the curve was used as a reference for the standardization of the power values with respect to a constant to the signal. The method allowed a better definition of the spectral profile than it is obtained by normalization vs. the total power value.

Adult↗
PubMed1996

The uses and abuses of meta-analysis.

Meta-analysis is a quantitative process of summary and interpretation which involves pooling information from independent studies concerning a single theme in order to draw conclusions. Greatly increased employment of meta-analysis is currently being advocated for clinical and policy decision making. However, the prestige of meta-analysis is based upon a false model of scientific practice. Interpreting empirical research is an extremely complex activity requiring clinical and scientific knowledge of the field in question; and teams of professional 'meta-analysts' with a primary skill base in information technology and biostatistics cannot take over this role. Meta-analysis is not a hypothesis-testing activity, and cannot legitimately be used to establish the reality of a putative hazard or therapy. The proper use of meta-analysis is to increase the precision of quantitative estimates of health states in populations. If used to estimate an effect, the reality of that effect should have been established by previous scientific studies. But the summary estimate from a meta-analysis can only be directly applied to a target population when the 'meta-protocol' and 'meta-population' match the target situation in all relevant particulars. These constraints can rarely be satisfied in practice, so the results of meta-analysis typically require adjustment--which is a complex, assumption-laden process that negates many of the statistical power advantages of a meta-analysis. Lacking any understanding or acknowledgement of the need for adjustment, most meta-analyses must be regarded as abuses of the technique.

Clinical Trials as Topic↗
PubMedDate not supplied

Analysis of subjective knee complaints using visual analog scales.

A questionnaire using a system of visual analog scales was developed for analyzing subjective knee complaints. This system was tested on 117 consecutive patients who had undergone knee surgery and 65 patients at their initial office evaluation of a knee disorder. The validity of and patient affinity for this type of questionnaire was compared with that of three other established subjective evaluation methods. The visual analog scale system was shown to be valid and comparable to other methods while offering several advantages. It brought greater sensitivity and greater statistical power to data collection and analysis by allowing a broader range of responses than did traditional categorical responses. It removed bias that was introduced by examiner questioning, and it allowed graphic temporal comparisons. Most importantly, patient affinity was higher for this type of subjective evaluation than for other methods.

Data Interpretation, Statistical↗
PubMed1999

An issue of statistical analysis in controlled multi-centre studies: how shall we weight the centres?

When analysing data from a controlled multi-centre study, an important issue is how to weight each centre to assess the overall treatment effect. The unweighted analysis, which weights all centres equally, was recommended by many statisticians and the U.S. Food and Drug Administration, and has been routinely utilized as the primary statistical method for many phase III clinical studies in the pharmaceutical industry. The weighted analysis, which weights centres relative to the number of patients in them, was considered not meaningful in the presence of treatment-by-centre interaction. This paper demonstrates why we should hesitate to use the unweighted analysis as the primary statistical method of a study from a statistical power perspective. It also shows that the weighted analysis is meaningful, even in the presence of treatment-by-centre interaction, and that it is generally the preferred approach.

Controlled Clinical Trials as Topic↗
PubMed1981

Multivariate data analysis for outcome studies.

The use of multivariate statistical techniques for analyzing the complex data often gathered in outcome studies is discussed. The multivariate analysis of variance (MANOVA) is suggested for multiple group studies common to outcome studies. This technique can be utilized for a large number of specific research designs whenever multiple outcome measures are collected. MANOVA offers two specific advantages over more familiar univariate approaches: it presents better control over Type 1 error rates while preserving statistical power, and it allows more thorough analysis of complex data.

Humans↗
PubMed2004

Meta-analysis: budesonide treatment for collagenous colitis.

BACKGROUND: Collagenous colitis is typified by chronic watery diarrhoea and characteristic histological alterations of the colonic mucosa without endoscopic abnormalities. Budesonide, a corticosteroid with high first-pass metabolism has been examined in collagenous colitis, but studies to date have had small numbers, and relatively low statistical power. AIM: A meta-analysis of existing published trials was undertaken to evaluate the treatment effect of budesonide in collagenous colitis. METHODS: All pertinent literature sources were searched for published reports in English of budesonide use in collagenous colitis. MEDLINE and EMBASE databases were reviewed, as well as bibliographies from published articles and available abstracts from relevant meetings. Literature that met prespecified criteria was selected for the meta-analysis. RESULTS: Three trials were included in the meta-analysis. Budesonide significantly decreased stool frequency (budesonide vs. placebo OR: 20.1, 95% CI: 7.0-57.5, P < 0.0001). In general, budesonide treatment was well-tolerated. CONCLUSIONS: Budesonide is clinically effective short-term in collagenous colitis, and seems to be relatively well-tolerated. Clinicians can consider this drug as a reasonable option for patients with this disorder.

Anti-Inflammatory Agents↗