1,721,004 research outputs found
Nonparametric tests in the unbalanced multivariate one-way design
No full textA nonparametric model for the multivariate one-way design is discussed which entails continuous as well as discontinuous distributions and, therefore, allows for ordinal data. Nonparametric hypotheses are formulated by the normalized version of the marginal distribution functions as well as the common distribution functions. The differences between the distribution functions are described by means of the so-called relative treatment effects, for which unbiased and consistent estimators are derived. The asymptotic distribution of the vector of the effect estimators is derived and under the marignal hypothesis a consistent estimator for the asymptotic covariance matrix is given. Nonparametric Versions of the Wald-type statistic, the ANOVA-type statistic and the Lawley-Hotelling statistic are considered and compared by means of a simulation study. Finally, these tests are applied to a psychiatric clinical trial
An exact paired rank test
No full textAn exact rank test for two dependent samples based on overall mid-ranks is discussed which can be applied to metric as well as to ordinal data. The exact conditional distribution of the test statistic given the observed vector of rank differences is determined. A recursion formula is given as well as a fast shift algorithm in SAS/IML code. Moreover, it is demonstrated that the paired rank test can be more powerful than other tests for paired samples by means of a simulation study. Finally, the test is applied to a psychiatric trial with longitudinal ordinal data
Nonparametric methods in multivariate factorial designs
No full textA nonparametric approach to the analysis of multivariate data is presented that is based on seperate rankings for different variables and extends the results of Akritas ct al. (1997. J. Amer. Statist. Assoc. 89, 336-343.) to multivariate designs. Factorial designs are considered including degenerate distributions as well as discontinuous distributions. The asymptotic normality of a linear combination of dependent linear rank score statistics is shown under rather weak assumptions. Wald-type and ANOVA-type statistics are derived and their properties are compared in simulation studies. The theory is applied to a completely randomised two-way layout. (C) 2000 Elsevier Science B.V. All rights reserved. MSG: 62G05, 62G10, 62G20, 62H10, 62H12, 62H15
The nonparametric Behrens-Fisher problem: Asymptotic theory and a small-sample approximation
No full textA generalization of the Behrens-Fisher problem for two samples is examined in a nonparametric model. It is not assumed that the underlying distribution functions are continuous so that data with arbitrary ties can be handled. A rank rest is considered where the asymptotic variance is estimated consistently by using the ranks over all observations as well as the ranks within each sample. The consistency of the estimator is derived in the appendix. For small samples (n(1), n(2) greater than or equal to 10), a simple approximation by a central t-distribution is suggested where the degrees of freedom are taken from the Satterthwaite-Smith-Welch approximation in the parametric Behrens-Fisher problem. It is demonstrated by means of a simulation study that the Wilcoxon-Mann-Whitney-test may be conservative or liberal depending on the ratio of the sample sizes and the variances of the underlying distribution functions. For the suggested approximation, however, it turns out that the nominal level is maintained rather accurately. The suggested nonparametric procedure is applied to a data set from a clinical trial. Moreover, a confidence interval for the nonparametric treatment effect is given
The multivariate nonparametric Behrens-Fisher problem
No full textIn this paper, we consider the multivariate case of the so-called nonparametric Behrens-Fisher problem where two samples with independent multivariate observations are given and the equality of the marginal distribution functions under the hypothesis in the two groups is not assumed. Moreover, we do not require the continuity of the marginal distribution functions so that data with ties and, particularly, multivariate-ordered categorical data are covered by this model. A multivariate relative treatment effect is defined which can be estimated by using the mid-ranks of the observations within each component and we derive the asymptotic distribution of this estimator. Moreover, the unknown asymptotic covariance matrix of the centered vector of the estimated relative treatment effects is estimated and its L-consistency is proved. To test the hypothesis of no treatment effect, we consider the rank version of the Wald-type statistic (as used in Puri and Sen, Nonparametric Methods in Multivariate Analysis, Wiley, New York, 1971) and the rank version of the ANOVA-type statistic which was suggested by Brunner et a]. [J. Amer. Statist. Assoc. 92 (1997) 1494-1502] for univariate nonparametric models. Simulations show that the ANOVA-type statistic appears to maintain the pre-assigned level of the test quite accurately (even for rather small sample sizes) while the Wald-type statistic leads to more or less liberal decisions. Regarding the power, none of the two statistics is uniformly superior to the other. (C) 2002 Elsevier Science B.V. All rights reserved
A prospective, randomized, sequential crossover trial of large-volume versus normal-volume leukapheresis procedures: effects on serum electrolytes, platelet counts, and other coagulation measures
No full textBACKGROUND: LVL procedures with the administration of heparin as an additional anticoagulant are increasingly performed because of the potentially higher yield of autologous peripheral blood HPCs. A prospective, randomized crossover trial was performed to evaluate the influence of leukapheresis volume-that is, large versus normal-on serum electrolytes, platelet count, and other coagulation measures in 25 patients with breast cancer and 14 patients with non-Hodgkin's lymphoma. STUDY DESIGN AND METHODS: Patients were randomly assigned to start either with an LVL on Day 1 followed by a normal-volume leukapheresis (NVL) on Day 2 or vice versa. In LVL, heparin was administered in addition to ACD-A. Bleeding complications, transfusion support, whole-blood counts, and several coagulation measures as well as plasma heparin levels were evaluated. RESULTS: Although the duration, the infused amount of ACD-A, the flow rate, the drop in platelet count, and the drop in potassium were significantly greater in LVL, and although LVL patients also received heparin, there was no significant difference in clinical tolerance or bleeding complications. After LVL, patients exhibited a significantly longer activated partial thromboplastin time (APTT), with a median of 70 seconds (range, 44-100 sec), and a median anti-factor Xa activity of 0.69 IU per mt (range, 0.10-1.29 IU/mL). The value of the APTT after LVL correlated with anti-factor Xa activity (r = 0.37, p<0.05), but not with platelet count or heparin infusion rate. Markers for coagulation activation did not increase during NVL or LVL. CONCLUSION: LVL with heparin as an additional anticoagulant seems to be a safe procedure in patients with low preleukapheresis platelet counts. No activation of coagulation occurred after NVL or LVL procedures
Spatial memory and learning deficits after experimental pneumococcal meningitis in mice
No full textSurvivors of bacterial meningitis frequently suffer from long-term sequelae, particularly from learning and memory deficits. For this reason, spatial memory and learning was studied in a mouse model of ceftriaxone-treated Streptococcus pneumoniae meningitis. Persistent deficits of spatial learning despite normal motor function were observed in mice infected with 10(4) colony-forming units (CFU) in 25 mul of saline into the right forebrain in comparison to mice treated with an equal amount of saline. Survivors of meningitis performed significantly worse in memorizing a hidden platform in a Morris water maze. After 2 weeks, the difference between post-meningitis and control mice diminished. Yet, when the platform was moved after 180 days, learning of the new location was still strongly impaired in mice surviving meningitis. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved
Fever of unknown origin: prospective comparison of [F-18]FDG imaging with a double-head coincidence camera and gallium-67 citrate SPET
No full textGallium-67 citrate is currently considered as the tracer of first choice in the diagnostic workup of fever of unknown origin (FUO). Fluorine-18 2'-deoxy-2-fluoro-D-glucose (FDG) has been shown to accumulate in malignant tumours but also in inflammatory processes. The aim of this study was to prospectively evaluate FDG imaging with a double-head coincidence camera (DHCC) in patients with FUO in comparison with planar and single-photon emission tomography (SPET) Ga-67 citrate scanning. Twenty FUO patients underwent FDG imaging with a DHCC which included transaxial and longitudinal whole-body tomography. In 18 of these subjects, Ga-67 citrate whole-body and SPET imaging was performed. The Ga-67 citrate and FDG images were interpreted by two investigators, both blinded to the results of other diagnostic modalities. Forty percent (8/20) of the patients had infection, 25% (5/20) had auto-immune diseases, 10% (2/20) had neoplasms and 15% (3/20) had other diseases. Fever remained unexplained in 10% (2/20) of the patients. Of the 20 patients studied, FDG imaging was positive and essentially contributed to the final diagnosis in 11 (55%). The sensitivity of transaxial FDG tomography in detecting the focus of fever was 84% and the specificity, 86%. Positive and negative predictive values were 92% and 75%, respectively. Tf the analysis was restricted to the 18 patients who were investigated both with Ga-67 citrate and FDG, sensitivity was 81% and specificity, 86%. Positive and negative predictive values were 90% and 75%, respectively. The diagnostic accuracy of whole-body FDG tomography (again restricted to the aforementioned 18 patients) was lower (sensitivity, 36%; specificity, 86%; positive and negative predictive values, 80% and 46%, respectively). Ga-67 citrate SPET yielded a sensitivity of 67% in detecting the focus of fever and a specificity of 78%. Positive and negative predictive values were 75% and 70%, respectively. A low sensitivity (45%), bur combined with a high specificity (100%), was found in planar Ga-67 imaging. Positive and negative predictive values were 100% and 54%, respectively. It is concluded that in the context of FUO, transaxial FDG tomography performed with a DHCC is superior to Ga-67 citrate SPET. This seems to be the consequence of superior tracer kinetics of FDG compared with those of Ga-67 citrate and of a better spatial resolution of a DHCC system compared with SPET imaging. In patients with FUO, FDG imaging with either dedicated PET or DHCC should be considered the procedure of choice
Screen film vs full-field digital mammography: image quality, detectability and characterization of lesions (vol 12, pg 1697, 2002)
No full textReduced release of DNA from Streptococcus pneumoniae after treatment with rifampin in comparison to spontaneous growth and ceftriaxone treatment
No full textIn order to study the release of DNA from Streptococcus pneumoniae in vitro during spontaneous growth and treatment with ceftriaxone or rifampin, a semiquantitative polymerase chain reaction was used. During spontaneous growth, high concentrations of bacterial DNA were released. Exposure to 10 mug/ml of ceftriaxone decreased the DNA release, in median, by 19 times (P=0.03 vs. spontaneous growth). Treatment with 10 mug/ml of rifampin led to a reduction of DNA release, in median, by a factor of 49 (P=0.03 vs. ceftriaxone; six experiments performed on different days)
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