Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Statistical Power”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38Linked to original sources
PubMed2006

Further clarification of the contribution of the tryptophan hydroxylase (TPH) gene to suicidal behavior using systematic allelic and genotypic meta-analyses.

Suicide is a major public health issue, especially in western countries, accounting for approximately 1 million deaths every year throughout the world. The tryptophan hydroxylase (TPH) gene has been extensively studied as a candidate for suicidal behavior due to its role in serotonergic neurotransmission. Since the first study associating the gene with schizophrenia, there have been many attempts to replicate it. However, a number of these studies have produced contrary results, possibly reflecting inadequate statistical power and the use of different populations. Association data relating European and, more particularly, Asian populations has become increasingly available in recent years. To examine whether the aggregate data provide evidence of statistical significance, the current meta-analysis has combined all the published studies up to July 2005, and examined the polymorphisms (A779C, A218C, A-6526G) in the context of varied suicidal behaviors by analyzing the studies in total and in subsets. Compared with the inconsistent results of previous studies, the current results (22 references) confirm a strong overall association between suicidal behavior and the A779C/A218C polymorphisms, supporting the involvement of TPH in the pathogenesis of suicidal behavior.

Gene Frequency↗
PubMed2005

The serotonin transporter length polymorphism, neuroticism, and depression: a comprehensive assessment of association.

BACKGROUND: A promoter-based length polymorphism (5-HTTLPR) of the human serotonin gene (SLC6A4) has exhibited inconsistent association with emotionality phenotypes, such as major depression (MD) and the personality trait neuroticism (N). Several explanations have been posited to account for this discrepancy, including underpowered experimental design and variation in gender ratio, age, and ethnicity. METHODS: Here, we describe three independent tests of association between the 5-HTTLPR locus and both N and MD in samples selected for extremeness of N-score from two homogenous populations (n = 88,142, and 20,921). Calculations of statistical power indicated that at a 5% alpha level, these samples retain 100% power to detect a genetic effect accounting for just .5% of phenotypic variance. Effects of age were regressed out of the phenotypic measure, and gender was included as a covariate. RESULTS: No statistically significant effects of genotype could be identified on either N or MD phenotypes (in all cases, p > or = .26), independently of the genetic mode of action applied. CONCLUSIONS: Our data do not support the hypothesis that the 5-HTTLPR variant contributes significantly toward human emotionality as indexed by either the Eysenck Personality Questionnaire N scale or the DSM-IV for MD.

Depression↗
PubMed1996

Monitoring and analysis of outcome studies.

Monitoring technology appears to be advancing at a rare that exceeds our ability to assess its effectiveness. RCTs are often poorly designed and lacks statistical power. Even high-quality RCTs may not provide inferences that can be generalized across all patient populations. Alternative methods of technology assessment, such as closed claims analysis, meta-analysis, and statistical process control, also have limitations. PORTs using a standard model of combined techniques are beginning to solve some of the more common methodological problems. The future of technology assessment relies on the ability to conduct large-scale cohort studies from routine practice settings. In terms of intraoperative monitors, this may require production of a complete and valid database of all monitored variables that can compared to a complete and valid database of all monitored variables that can be compared to a complete and valid database of appropriate outcome indicators. National standard for collection of data need to be developed. At this time, professional societies should focus more on developing guidelines for technology assessment than on guidelines for technology utilization.

Cohort Studies↗
PubMed1997

Mexiletine in the symptomatic treatment of diabetic peripheral neuropathy.

OBJECTIVE: To evaluate the efficacy and safety of mexiletine in the symptomatic treatment of diabetic peripheral neuropathy (DPN). METHODS: In this prospective, double-blind study, 29 patients were randomized to receive mexiletine 600 mg/d or matching placebo for 3 weeks. A four-item symptom score (FIS), which rated pain, dysesthesias, paresthesias, and nightly exacerbations of symptoms, and a 100-mm visual analog scale (VAS), which rated pain intensity, were completed by patients before and after treatment. At the end of treatment independent patient and investigator global assessments were made. Patients reported adverse effects after 1 and 3 weeks of treatment. RESULTS: Treatment groups were similar at baseline. The difference between the median changes in FIS scores (mexiletine = 5.5, placebo = 2) was not statistically significant. Overall symptom response was similar in both treatment groups as demonstrated by both global assessments (p = 0.19). The mean change in VAS score from baseline to posttreatment was determined for both groups and the difference between these mean scores was 16.5 mm (95% CI, -7.1 to 40.2 mm) (p = 0.16). Inadequate statistical power (1-beta = 0.40) may have resulted from small sample size, small magnitude of effect, or variability in the measured effect. Adverse effects were more common in the mexiletine group, though not statistically significant. One patient receiving mexiletine was hospitalized for palpitations. CONCLUSIONS: Because of conflicting reports of mexiletine's efficacy in the treatment of symptomatic DPN, this drug should be reserved for patients unresponsive or intolerant to standard therapy, without evidence of heart disease, and with sensations of burning heat, formication, or stabbing pain.

Adult↗
PubMed2006

Sterilizing effects of the Erbium:Yag laser upon dental structures: an in vitro study.

AIM: An evaluation was made of the sterilizing effects of the Erbium:YAG laser at different power ratings upon dental structures in vitro. DESIGN: An in vitro study was made of 47 single-root teeth removed for periodontal reasons in the Oral and Maxillofacial Surgery Teaching Unit (Department of Medicine and Orofacial Surgery, Madrid Complutense University Dental School, Spain). The teeth were divided into three laser irradiation groups (250, 350 and 450 mJ) and a non-irradiated control group. The teeth were then immersed in an enrichment medium for 72 hours under conditions of anaerobiosis, with visual controls after 24, 48 and 72 hours. Posteriorly, microbiological cultures were made in blood agar to confirm the results of the visual inspections. RESULTS: Increased percentage sterilization of the samples was recorded with increasing irradiation power - statistically significant differences being observed between all irradiated groups versus the controls. CONCLUSIONS: The Erbium:YAG laser exerts a sterilizing effect upon dental structures in vitro. This effect increases with increasing laser power ratings.

Humans↗
PubMed1986

Study duration in antidepressant research: advantages of a 12-week trial.

There has been an increasing interest in studying the effectiveness of antidepressants in non-melancholic depressives. For non-melancholic patients who are characterized by transient mood improvement, a single cross-sectional evaluation may reflect temporary change. Transient improvement, like any source of instability in an outcome measure, reduces validity and consequently power. To minimize the effects of transient mood change in non-melancholic depressives, we designed a two-phase drug trial. The first phase was a standard 6-week trial. Those judged responders at the end of the first phase entered the second 6-week phase. Between weeks 6 and 12 it was anticipated that a smaller proportion of six-week responders would relapse on drug than placebo, thus sharpening the contrast between treatments. The purpose of this paper is to demonstrate the power advantages of the 12-week design. Data is presented which suggests that a 12-week design reduces transient improvement, increases treatment effect size, and requires a smaller number of patients for equivalent statistical power. It also offers a better estimate than a 6-week study of the proportion of patients who will have persistent clinical benefit.

Adolescent↗
PubMed2003

Revascularization in patients with coronary artery disease, left ventricular dysfunction, and viability: a meta-analysis.

BACKGROUND: The effects of viability status and treatment allocation on long-term mortality in patients with left ventricular dysfunction and coronary artery disease have not been determined. Several observational studies with significant limitations have addressed this issue, and a recent meta-analysis has attempted to combine these results to increase statistical power. However, the analysis did not test for an interaction between viability status and treatment type, and included extraneous studies. We provide an alternate meta-analysis of this primary literature, utilizing interaction statistical methodology on relevant data and factoring in multiple limitations. METHODS: We examined papers from this prior meta-analysis examining viable and nonviable patients undergoing surgical or medical therapy. We determined an interaction odds ratio for each study and used an empirical Bayes random-effects model to obtain a combined interaction odds ratio that was tested for statistical significance. We compared our results against an interaction odds ratio we estimated from the primary studies included in the previous meta-analysis. RESULTS: Nine relevant studies with 1244 patients and 172 events were identified that utilized all 4 treatment/viability subsets. The interaction odds ratio was 2.76 (P =.0176, 95% CI 1.19-6.38), 2.5 times lower than our estimated interaction odds ratio of 7.27 for the prior meta-analysis. CONCLUSIONS: We found a markedly reduced but statistically significant interaction between viability status and treatment allocation. However, numerous limitations in the primary studies and the application of meta-analysis along with significant improvements in medical therapies render a randomized controlled trial necessary to reach a definitive conclusion to this critical question.

Coronary Artery Disease↗
PubMed2004

Incorporating genotyping uncertainty in haplotype inference for single-nucleotide polymorphisms.

The accuracy of the vast amount of genotypic information generated by high-throughput genotyping technologies is crucial in haplotype analyses and linkage-disequilibrium mapping for complex diseases. To date, most automated programs lack quality measures for the allele calls; therefore, human interventions, which are both labor intensive and error prone, have to be performed. Here, we propose a novel genotype clustering algorithm, GeneScore, based on a bivariate t-mixture model, which assigns a set of probabilities for each data point belonging to the candidate genotype clusters. Furthermore, we describe an expectation-maximization (EM) algorithm for haplotype phasing, GenoSpectrum (GS)-EM, which can use probabilistic multilocus genotype matrices (called "GenoSpectrum") as inputs. Combining these two model-based algorithms, we can perform haplotype inference directly on raw readouts from a genotyping machine, such as the TaqMan assay. By using both simulated and real data sets, we demonstrate the advantages of our probabilistic approach over the current genotype scoring methods, in terms of both the accuracy of haplotype inference and the statistical power of haplotype-based association analyses.

Algorithms↗
PubMed1992

Statistical method for estimating the standard errors of branch lengths in a phylogenetic tree reconstructed without assuming equal rates of nucleotide substitution among different lineages.

A statistical method is developed for estimating the standard errors of branch lengths in a phylogenetic tree reconstructed without assuming equal rates of nucleotide substitution among different lineages. This method can be easily used for testing whether the length of an interior branch in a reconstructed tree is positive, i.e., whether the topology of the tree is correct. Computer simulations indicate that this method is appropriate for a statistical test. As an example, this method is applied to phylogenetic trees reconstructed for the four hominoid species: human, chimpanzee, gorilla, and orangutan. The results obtained show that the present method provides a powerful statistical test.

Animals↗
PubMed1999

Litter effects on caries in rats and implications for experimental design.

The purpose of this study was to obtain quantitative estimates of litter effects on caries development in rats and to examine the implications for design of rat caries experiments. Twelve female Sprague-Dawley rats, aged 60 days, were bred with 4 male rats. Nine of the 12 dams had litters in close proximity. The litters were culled to 10 pups. One pup from each litter was placed with each of the other dams for nursing, leaving 2 pups from each litter with the birth dam. This design allowed the litter effect to be separated into a prenatal component, reflecting the shared genetic makeup and in utero environment of littermates, and a postnatal component reflecting a shared environment from shortly after birth to weaning. Pups were infected with Streptococcus sobrinus and fed Diet 2000 and 10% (w/v) sucrose water for 5 weeks. There was no significant evidence of a postnatal litter effect for smooth surface caries (p = 0.37) or sulcal caries (p = 0.43). The prenatal litter effect was significant for both smooth surface caries and sulcal caries (p<0. 01). When litter effects are present, the statistical power of caries studies is improved if animals from the same litter are divided evenly among experimental groups. In addition, if litter effects are present but not allowed for in data analysis, incorrect statistical inferences may be drawn. Based on our results and other reports of litter effects, we recommend planning for litter effects in the design and analysis of rat caries studies.

Animals↗
PubMed1993

Meta-analysis as a guide to clinical practice.

BACKGROUND: Meta-analysis is now widely used in order to increase the power of individual clinical studies. Important far-reaching conclusions have been derived by pooling the results of studies which in isolation would not be large enough to reach definitive conclusions. While the statistical power is thereby amplified, so is the potential for error. OBJECTIVE: To assess the potential and the pitfalls of meta-analysis as a guide to clinical practice. CONCLUSIONS: Conclusions derived from meta-analysis may be influenced by unrecognized selection bias and heterogeneity of studies included. Publication of the results may be in a form which does not lend itself readily to critical analysis and misleading results may therefore be accepted.

Antihypertensive Agents↗
PubMed2000

A simulator for evaluating methods for the detection of lesion-deficit associations.

Although much has been learned about the functional organization of the human brain through lesion-deficit analysis, the variety of statistical and image-processing methods developed for this purpose precludes a closed-form analysis of the statistical power of these systems. Therefore, we developed a lesion-deficit simulator (LDS), which generates artificial subjects, each of which consists of a set of functional deficits, and a brain image with lesions; the deficits and lesions conform to predefined distributions. We used probability distributions to model the number, sizes, and spatial distribution of lesions, to model the structure-function associations, and to model registration error. We used the LDS to evaluate, as examples, the effects of the complexities and strengths of lesion-deficit associations, and of registration error, on the power of lesion-deficit analysis. We measured the numbers of recovered associations from these simulated data, as a function of the number of subjects analyzed, the strengths and number of associations in the statistical model, the number of structures associated with a particular function, and the prior probabilities of structures being abnormal. The number of subjects required to recover the simulated lesion-deficit associations was found to have an inverse relationship to the strength of associations, and to the smallest probability in the structure-function model. The number of structures associated with a particular function (i.e., the complexity of associations) had a much greater effect on the performance of the analysis method than did the total number of associations. We also found that registration error of 5 mm or less reduces the number of associations discovered by approximately 13% compared to perfect registration. The LDS provides a flexible framework for evaluating many aspects of lesion-deficit analysis.

Brain↗
PubMed1999

Why do we need randomized and epidemiological studies on cardiovascular disease? Evidence-based cardiology VII.

Over the last two decades the results of randomized clinical studies, which are powerful aids for correctly assessing therapeutical strategies, have consolidated cardiological practice. In addition, scientifically interesting hypotheses have been generated through the results of epidemiological studies. Properly conducted randomized studies without systematic errors and with statistical power adequate for demonstrating moderate and reasonable benefits in relevant clinical outcomes have provided reliable and strong results altering clinical practice, thus providing adequate treatment for patients with cardiovascular disease (CVD). The dissemination and use of evidence-based medicine in treating coronary artery disease (CAD), heart failure (HF), and in prevention will prevent hundreds of thousands of deaths annually in developed and developing countries. CVD is responsible for approximately 12 million deaths annually throughout the world, and approximately 60% of these deaths occur in developing countries. During recent years, an increase in mortality and morbidity rates due to CVD has occurred in developing countries. This increase is an indication that an epidemiological (demographic, economical, and health-related) transition is taking place in developing countries and this transition implies a global epidemic of CVD, which will require wide-ranging and globally effective strategies for prevention. The identification of conventional and emerging risk factors for CVD, as well as their management in high-risk individuals, has contributed to the decrease in the mortality rate due to CVD. Through a national collaboration, several multi-center and multinational randomized and epidemiological studies have been carried out throughout Brazil, thus contributing not only to a generalized scientific growth in different Brazilian hospitals but also to the consolidation of an increasingly evidence-based clinical practice.

Cardiology↗
PubMed1999

Improved auditory cortex imaging using clustered volume acquisitions.

The effects of the noise of echo-planar functional magnetic resonance imaging on auditory cortex responses were compared for two methods of acquiring functional MR data. Responses observed with a distributed volume acquisition sequence were compared to those obtained with a clustered volume acquisition sequence. In the former case, slices from the volume were acquired at equal intervals within the repetition time, whereas the latter acquired all slices in rapid succession at the end of the imaging period. The clustered volume acquisition provides a period of quiet during which a stimulus may be presented uninterrupted and uncontaminated by the noise of echo-planar imaging. Both sequences were implemented on a General Electric Signa imager retrofitted for echo-planar imaging by Advanced NMR Systems, Inc. The sequences were used to acquire 60 images per slice of a fixed volume of cerebral cortex while subjects were presented an instrumental music stimulus in an On vs. Off paradigm. Data were acquired for both sequences using TR values of 2, 3, 4, 6 and 8 sec. The clustered volume acquisition sequence was found to yield greater measures of dynamic range (percent signal change, mean statistical power per unit imaging time) across the tested range of TR values. Observations of more consistent spatial extent of responses, greater mean signal changes, and higher and more consistent values of mean t-statistic per unit imaging time demonstrate the efficacy of using a clustered volume acquisition for fMRI of auditory cortex.

Adult↗
PubMed1989

Power analyses of moment analysis parameter in bioequivalence tests.

Simulated and experimental data were used to evaluate the mean residence time (MRT) as a parameter for estimating the rate of bioavailability in bioequivalence tests and to compare MRT with tmax (the time of peak drug concentration), both pharmaceutically and statistically. Although the values of MRT were more dependent on the elimination rate constant than tmax, MRTs were sufficiently sensitive to variations in the absorption rate. The statistical power of MRT infinity obtained by an extrapolation method was lower (especially when the flip-flop phenomenon occurred) than that of MRTt (calculated using data from zero time through the last sampling time). However, the power of MRTt was shown to be comparable to or higher than that of either AUCt or Cmax (the peak drug concentration) from simulated data. These results were also confirmed experimentally using previously obtained data. The effect of variances of plasma concentrations on the power of these parameters was also studied using a simulation technique. Even large variances near the last sampling time did not substantially affect the power of MRTt. Thus MRTt can be used as a parameter for estimating the rate of bioavailability from dosage forms in place of tmax in bioequivalence tests.

Biological Availability↗
PubMed1994

Design and analysis considerations in a cohort study involving repeated measurement of both exposure and outcome: the association between genital papillomavirus infection and risk of cervical intraepithelial neoplasia.

Cohort studies commonly involve a single determination of exposure, and one or more assessments of whether or not the outcome of interest has occurred. This approach is appropriate when the exposure does not change with time, and when one can readily determine the time of outcome (for example, mortality). If either of these conditions is not met, however, we may introduce bias into the estimate of effect, since we may misclassify individual members of the cohort with respect to exposure, outcome or both. We can reduce this bias by measuring exposure and outcome on more than one occasion. In this paper, we illustrate the design and analysis issues that arise in such circumstances, by reference to an ongoing prospective study of the relationship between genital papillomavirus infection and risk of cervical intraepithelial neoplasia. This study entails annual assessments of the status of the study subjects with respect to both conditions. In particular, we examine the implications that use of this design has on the statistical power of the study.

Adult↗
PubMed2005

[National cohort of patients with emphysema and alpha-1 antitrypsin deficiency].

BACKGROUND: The natural history and optimal therapeutic management of emphysema associated with alpha-1 antitrypsin deficiency are poorly understood. The purpose of this cohort of patients with emphysema associated with alpha-1 antitrypsin deficiency is to describe their characteristics and to study the factors associated with the evolution of their pathology. MATERIALS AND METHODS: It is a multicentre, prospective, cohort study including all the patients in metropolitan France with alpha-1 antitrypsin deficiency associated with emphysema (diagnosed by CT scanning) and an obstructive ventilatory defect. All respiratory physicians will be approached. Patients meeting the inclusion criteria will be followed up every 6 months for 5 years. Clinical and spirometric data as well as those relating to quality of life will becollected. The principal criterion will be FEV1; the secondary criteria: quality of life, exacerbations requiring hospitalistion and mortality. EXPECTED RESULTS AND VIEWPOINTS: 300-500 patients are expected to be included. At the conclusion incorporation of this cohort into AIR (Alpha-antitrypsin International Registry) will increase the statistical power. This study could also provide the base for prospective trials and research projects.

Adolescent↗
PubMed1990

Nonparametric estimation of degenerate ROC data sets used for comparison of imaging systems.

Maximum likelihood estimation, assuming a binormal model, has been used extensively to estimate the area under receiver operating characteristic (ROC) curves and thus provide an index of diagnostic accuracy for the comparison of two imaging systems. However, in some instances, a degenerate data set results in a fitted ROC curve of inappropriate shape. In those instances, a nonparametric Wilcoxon statistic may be used to compare the areas under two ROC curves. Simulation of this approach indicates that the procedure has relatively high statistical power and its use in specific degenerate data sets shows its applications potential.

Data Interpretation, Statistical↗