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Results for “Statistical power analysis”

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PubMed1994

The diagnosis of visual field progression in glaucoma.

The detection of true visual field deterioration in glaucoma is of fundamental importance but is limited by inherent variability of the measurements. New techniques have been developed that use powerful statistical regression analysis methods to objectively quantify progression of visual field defects. These have been combined with new methods of graphical presentation to reveal the spatial distribution in the visual field of deterioration. New measurement techniques utilizing blue-on-yellow, flicker, and motion stimuli provide further advantages and may be combined with regression analysis to improve the early detection of real progression of visual field loss.

Glaucoma↗
PubMed2002

The F158V polymorphism in FcgammaRIIIA shows disparate associations with rheumatoid arthritis in two genetically distinct populations.

OBJECTIVES: To investigate the association of the FcgammaRIIIA gene with rheumatoid arthritis (RA) in two genetically distinct groups: a white group from the United Kingdom and a northern Indian group. METHODS: The distributions of the two alleles of the FcgammaRIIIA F158V polymorphism were determined in 398 white patients from the United Kingdom and 63 Indian patients with RA and compared with those from 289 United Kingdom and 93 Indian healthy controls, respectively. RESULTS: Among the Indian patients, the frequency of the rare 158V allele and the proportion of 158VV homozygotes were reduced (relative risk (RR)=0.3, 95% confidence interval (95% CI) 0.1 to 1.1, p<0.06), reaching statistical significance for carrying the 158VV phenotype relative to 158FV or FF (RR=0.2, 95% CI 0.05-0.9, p<0.02). Conversely, no significant deviation in allelic frequencies was noted between the patients and controls from the United Kingdom. CONCLUSIONS: The 158VV phenotype showed a weak protective effect against developing RA in the Indian group. However, this sample was small (resulting in a low power for statistical analysis) and no independent confirmation was found in the larger white United Kingdom group. Thus the FcgammaRIIIA locus is unlikely to be of major importance in causing RA.

Alleles↗
PubMed1993

Quality of life assessment for evaluating benign prostatic hyperplasia treatments. An example of using a condition-specific index.

546 patients enrolled in a prospective study of patient treatment choices for benign prostatic hyperplasia (BPH) completed a self-administered questionnaire that included a symptom index, two general measures of quality of life, and a condition-specific measure of the impact of BPH symptoms on patient quality of life. As expected, differences in symptoms of BPH were significantly associated with general measures of quality of life and the condition-specific impact score. However, the condition-specific impact score was more sensitive to differences in symptoms than the general measures. Hence, such measures are likely to be more responsive to treatment effects, may provide more power for statistical analysis, and hence should be considered along with general quality of life measures for use in treatment outcome studies.

Aged↗
PubMedDate not supplied

Serum lipoprotein levels fail to predict postangioplasty recurrent coronary artery stenosis.

A prospective study to explore the role of serum lipoproteins in the development of recurrent stenosis after percutaneous transluminal coronary angioplasty was conducted on serum samples from 103 patients. Serum was collected at the time of angioplasty and evaluated for total cholesterol, total triglycerides (TG), high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, very low-density lipoprotein cholesterol, and apolipoproteins A1 and B. In addition, LDL cholesterol/HDL cholesterol ratios and apolipoprotein B/A1 ratios were calculated for each sample. Information was then gathered from four years of follow-up after angioplasty, which was sufficient to establish the presence or absence of recurrent stenosis in 87 patients (68 males and 19 females). Stenosis recurred in 31 of the 87 patients (36%); the rate was similar for males (35%) and females (37%). Univariate analysis of the total patient population revealed no statistically significant difference in values for any of these lipoprotein parameters between success and recurrence groups. Likewise, multivariate analysis revealed no combination of lipoprotein values to be associated with success or recurrence. Findings were similar for the males alone and the total group of males and females. The female group was too small for separate statistical analysis. The power of this study to detect meaningful differences in each of these parameters except TG was at least 80%. These results do not support the hypothesis that lipoprotein factors influence the development of recurrent stenosis in patients undergoing coronary angioplasty.

Angioplasty, Balloon↗
PubMed1997

An under-occluded roller pump is less hemolytic than a centrifugal pump.

The purpose of this study is to measure and compare the hemolysis produced by roller pumps with varied occlusion settings and a centrifugal pump. The null hypothesis is that there is no difference in the Index of Hemolysis (IH = gm Hb/100 L pumped) produced by a roller pump (RP) at four different occlusion settings and a centrifugal pump (CP) at the same blood flow rate (4.5 L/min) and afterload (250 mmHg, +/-10 mmHg) over three hours. Five identical closed-loop circuits were assembled and primed with saline. The pumps were then calibrated and occlusions were set. In three circuits, the occlusion for the RP was opened at 5 RPMs to support 150, 225, or 300 mmHg (+/-10 mmHg) against a clamped line. In one circuit, a RP was adjusted to a barely non-occlusive setting (1 cm drop/30 inch gradient). The fifth circuit employed a CP. Prior to testing, the saline in each circuit was replaced with one liter of fresh bovine blood (Hct = 22 +/- 2%). The IH for each treatment was compared in six trials yielding a statistical power > 0.80. Analysis of variance with multiple comparison (p < or = 0.05) demonstrated that compared to the barely non-occlusive setting, the IH in the centrifugal pump was not significantly greater. Under-occluded RP settings yielded IHs significantly less than the CP. It appears that opening the occlusion on a roller pump allows a lower IH compared to traditional RP occlusion setting or centrifugal pumping.

Animals↗
PubMed1987

The National Bladder Cancer Study: employment in the chemical industry.

The relationship between bladder cancer employment in the chemical industry was assessed in a study of 2,982 incident cases and 5,782 population controls. There were 190 cases and 369 controls who had ever been employed in the chemical industry [odds ratio (OR) = 1.0; 95% confidence interval (CI) = 0.8, 1.2]. Employment in the production of organic chemicals was associated with a 1.3-fold increased risk among men (95% CI = 0.8, 2.1). Risk increased with duration of employment, reaching an OR of 2.4 for 20 or more years (chi for trend = 1.57; P = .06). Women who had worked in the plastics industry had a 3.3-fold increased bladder cancer risk. Within the plastics and rubber industry, increased risks for bladder cancer were found for men in mixing, filtering, grinding, and other dusty operations (OR = 4.6; 95% CI = 1.0, 20.4) and men in heat-associated operations (OR = 2.8; 95% CI = 0.5, 15.3). A 1.4-fold risk among men in agricultural chemicals was attributable to risks in the pesticides subdivision (OR = 2.3; 95% CI = 0.6, 8.2). Men performing dusty operations (i.e., mixing, filtering, sifting, grinding, and crushing) in any industry had an OR of 1.4 (95% CI = 0.8, 2.7). Despite the large number of study subjects, few statistically significant findings were observed and should be evaluated with consideration of the large number of comparisons made in the analysis. The statistical power of case-control studies to detect risks associated with particular occupational exposures is limited by the small proportion of the population employed in any specific occupation or industry.

Adult↗
PubMedDate not supplied

Influence of number of surfaces and observers on statistical power in a multiobserver ROC radiographic caries detection study.

The aim of the study was to evaluate the influence of the number of surfaces (N(SURF)) and the number of observers (N(OBS)) on the statistical power of a study comparing the diagnostic accuracies of radiographic systems used for approximal caries lesion detection. A data set consisting of 338 surfaces examined by 10 independent observers using four radiographic systems was available. The presence of a caries lesion was assessed from a 5-point confidence scale. The true lesion diagnosis was established by histological validation. ROC curve areas (A(z)s) were used to express the diagnostic accuracy of the observers with the radiographic systems. Assuming that the A(z)s were tested by a two-way analysis of variance, we performed a simulation study in order to evaluate how the power of this statistical analysis depended on N(SURF) and N(OBS). As a measure of the statistical power we used the standard error of the difference between the expected A(z)s of two systems. The simulations were made with N(SURF) in the range from 25 to 338 and N(OBS) from 2 to 10. The simulations showed that the power increased as a function of the total number of evaluations per system (N(SURF) x N(OBS)), but how this number was attained in relation to the number of surfaces and observers had only marginal influence on the power. Thus, from a statistical point of view it may be concluded, provided that data are analyzed by a two-way analysis of variance, that study designs for comparing the accuracy of several systems can be composed freely in relation to the number of surfaces and observers as long as the total number of evaluations per system are identical.

Analysis of Variance↗
PubMed2004

Effects of censoring on parameter estimates and power in genetic modeling.

Genetic and environmental influences on variance in phenotypic traits may be estimated with normal theory Maximum Likelihood (ML). However, when the assumption of multivariate normality is not met, this method may result in biased parameter estimates and incorrect likelihood ratio tests. We simulated multivariate normal distributed twin data under the assumption of three different genetic models. Genetic model fitting was performed in six data sets: multivariate normal data, discrete uncensored data, censored data, square root transformed censored data, normal scores of censored data, and categorical data. Estimates were obtained with normal theory ML (data sets 1-5) and with categorical data analysis (data set 6). Statistical power was examined by fitting reduced models to the data. When fitting an ACE model to censored data, an unbiased estimate of the additive genetic effect was obtained. However, the common environmental effect was underestimated and the unique environmental effect was overestimated. Transformations did not remove this bias. When fitting an ADE model, the additive genetic effect was underestimated while the dominant and unique environmental effects were overestimated. In all models, the correct parameter estimates were recovered with categorical data analysis. However, with categorical data analysis, the statistical power decreased. The analysis of L-shaped distributed data with normal theory ML results in biased parameter estimates. Unbiased parameter estimates are obtained with categorical data analysis, but the power decreases.

Computer Simulation↗
PubMed1984

Advantages of integrated trials for performing multiple Phase II studies.

Phase II trials can be conducted in an integrated fashion that minimizes assignment of patients to potentially ineffective treatments. The technique allows definitions of response to include survival; earlier identification of more effective drugs; and completion of more Phase II studies in a given time period. It also encourages investigators to analyse results promptly. Because the analysis of each trial is independent, the statistical power of the analysis of results is retained. Identified shortcomings of the method include the need for a central mechanism to assign patients to treatment, the need for several drugs to be tested, physicians' uncertainty about which drug a particular patient will receive, and the increased time it may take to complete an individual trial.

Antineoplastic Agents↗
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

Powerful allele sharing statistics for nonparametric linkage analysis.

Nonparametric linkage analysis is widely used to map susceptibility genes for complex diseases. This paper introduces six nonparametric statistics for measuring marker allele sharing among the affected members of a pedigree. We compare the power of these new statistics and three previous statistics to detect linkage with Mendelian diseases having recessive, additive, and dominant modes of inheritance. The nine statistics represent all possible combinations of three different IBD scoring functions and three different schemes for sampling genes among affecteds. Our results strongly suggest that the statistic T(rec)(blocks) is best for recessive traits, while the two statistics T(kin)(pairs) and T(all)(kin) vie for best for an additive trait. The best statistic for a dominant trait is less clear. The statistics T(kin)(pairs) and T(all)(kin) are equally promising for small sibships, but in extended pedigrees the statistics T(dom)(blocks) and T(dom)(pairs) appear best. For a complex trait, we advocate computing several of these statistics.

Alleles↗
PubMed1988

Using the maximum test statistic in the two-period crossover clinical trial.

In a two-period crossover trial where residual carryover is suspected, it is often advised that first-period data only be used in an analysis appropriate for a parallel design. However, it has been shown (Willan and Pater, 1986, Biometrics 42, 593-599) that the crossover analysis is more powerful than the parallel analysis if the residual carryover, expressed as a proportion of treatment effect, is less than 2- square root of 2(1 - rho), where rho is the intrasubject correlation coefficient. Choosing between the analyses based on the empirical evaluation of this condition is equivalent to choosing the analysis with the larger corresponding test statistic. Approximate nominal significance levels are presented that maintain the desired level when basing the analysis on the maximum test statistic. Furthermore, the power and precision of the analysis based on the maximum test statistic are compared to the crossover and parallel analyses.

Clinical Trials as Topic↗
PubMedDate not supplied

Cerebral ischemia-reperfusion injury: a novel therapeutic approach with TAK-218.

The goal of the present study was to evaluate the potential neuroprotective effect of TAK-218 in an in vivo rat focal cerebral ischemia/reperfusion model. TAK-218 is a novel compound with multiple antiischemic properties, including suppression of aberrant dopamine release, modulation of sodium channels, and inhibition of lipid peroxidation. The study was a blinded, randomized, placebo-controlled study of TAK-218 in a three-vessel focal ischemic rat model. A total of 22 rats were randomly assigned to the treatment or placebo group. Animals were injected intrapertoneally with either a 2 mg/kg dose of drug or saline at 2 hours after reperfusion. Infarction volume was measured with use of 2,3,5-triphenyltetrazolium chloride. Total adjusted infarction volume in treated animals decreased by 10%. With use of a statistical analysis requiring 80% power with a 20% reduction desired effect, there was no statistically significant difference in the end-point of infarction volume between drug and placebo treatment groups. In light of the proven efficacy of thrombolytic therapy for acute stroke, it is now desirable to test neuroprotective agents during the 3-hour therapeutic window after ischemia. Further research is necessary to discern if a therapeutic agent with multiple antiischemic properties may provide a more robust neuroprotective effect than an agent with a single neuroprotective action.

Animals↗
PubMed2006

Can a meta-analysis answer the question: is mucosectomy and handsewn or double-stapled anastomosis better in ileal pouch-anal anastomosis?

Although ileal pouch-anal anastomosis (IPAA) is the procedure of choice for polyposis and ulcerative colitis with medically refractory disease or dysplasia, controversy exists concerning whether mucosal preservation with double-stapled (DS) IPAA is superior to mucosectomy and handsewn (HS) IPAA anastomosis for postoperative function. Prospective studies have shown no statistically significant differences. The use of meta-analysis can strengthen statistical power by combining the data from related studies. A meta-analysis was performed to determine whether there was a significant difference in functional and manometric outcome between HS-IPAA and DS-IPAA. Prospective, randomized studies were identified using a literature search. Functional outcome variables included number of normal continence, minor incontinence, nocturnal evacuation, the ability to discriminate flatus from stool, and antidiarrheal medication. Manometric outcomes included postoperative resting and squeeze anal pressures. Four prospective, randomized trials were identified. Of the 184 total patients, the HS-IPAA group included 86 patients (48 men and 38 women) and the DS-IPAA group included 98 patients (49 men and 49 women). There were no significant differences in functional outcome between HS-IPAA and DS-IPAA. In addition, there was no significant difference in sphincter resting and squeeze pressures between the two patient groups. This meta-analysis demonstrates that DS-IPAA offers no advantage in functional or manometric outcome when compared with HS-IPAA.

Adolescent↗
PubMed1994

[Meta-analysis and its application in epidemiology].

Meta-analysis provides a powerful statistical tool for epidemiological study. The basic principle of meta-analysis is introduced in this paper, and some problems about its application in epidemiology are discussed. This method was used by the authors to study the relationship between exposure to extreme low frequency electromagnetic fields (ELF) and childhood leukemia, and the result showed that there is a significant association between them.

Electromagnetic Fields↗