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Results for “Statistics, Nonparametric”

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PubMed2002

A case study of strategic infarct dementia investigated with the cognitive assessment system.

Two subjects with brain lesions who were matched on demographic variables were tested on the Cognitive Assessment System (CAS). AK had been dependent on caregivers after a frontal aneurysm 6 years previously despite intact receptive and expressive language skills and motor functions. GM sustained multiple infarcts although he continued to function well on his own. Nonparametric analysis showed that AK's T scores on CAS subtests were lower than that of GM's based on a comparison with a heterogeneous group of brain-damaged patients (p < .003). The CAS's broad range of complexity of items within subtests, apparent sensitivity in differentiating rates of cognitive decline in dementia, and convergence with dementia rating scales suggests that it could be useful for assessment of strategic infarct dementia.

Cerebral Infarction↗

PubMed1998

Mapping of the human insulin receptor substrate-2 gene, identification of a linked polymorphic marker and linkage analysis in families with Type II diabetes: no evidence for a major susceptibility role.

Insulin receptor substrate 2 (IRS-2) is a substrate of the insulin receptor and mediates the action of the insulin. Disruption of the IRS-2 gene in mice results in peripheral insulin resistance and relative insulin deficiency. It is therefore possible that defects in the IRS-2 gene contribute to Type II (non-insulin-dependent) diabetes mellitus. We have examined the gene for evidence of linkage to Type II diabetes in Ashkenazi Jewish families. Radiation hybrid panel mapping was used to refine the map position of the IRS-2 gene and, in the absence of polymorphic markers within the gene, to identify nearby markers. The IRS-2 gene was placed 23cR from the marker D13S1265 on chromosome 13q34. 200 affected sib-pairs were genotyped for three markers across the region. Nonparametric linkage analysis (GENEHUNTER) used with this data found no evidence of excess allele sharing in the IRS-2 gene region. We therefore concluded that variation in the IRS-2 gene is unlikely to contribute to Type II diabetes in this discrete Caucasian population.

Animals↗

PubMed2005

A nonparametric comparison of the effectiveness of treatments: a multivariate toxicity-penalized approach.

In cancer clinical trials, the amount of treatment dose actually received by a patient may be limited by severe toxicity or lack of efficacy. A nonparametric approach is proposed for comparing the effectiveness of treatments based on the bivariate relationship defined by the doses at which efficacy and toxicity are observed to occur. Simulation studies are used to contrast the performance of the new procedure with the usual method of comparing percentages of patients who have effective results. Data from a randomized clinical trial of patients with metastatic nonseminomatous germ cell tumors are used to illustrate the method.

Antineoplastic Agents↗

PubMed2004

Augmentation of electroconvulsive therapy seizures with sleep deprivation.

Electroconvulsive therapy (ECT) is the fastest and most effective treatment for severe or treatment-resistant affective and psychotic disorders. Its therapeutic effect is obtained through a generalized tonic-clonic seizure of adequate duration. Several factors (older age, male gender, and the sessions of ECT themselves) increase seizure threshold and reduce seizure time. In our work, sleep deprivation was used as a strategy to enhance the ECT seizure. A matched sample design was conducted on the basis of the following variables: gender, age range, and seizure threshold. After the first ECT, when the initial seizure threshold was measured, subjects were assigned to ECT (electroconvulsive therapy) or SD+ECT (sleep deprivation + electroconvulsive therapy). Changes in the variable of seizure threshold were studied in both groups during the treatment course. A nonparametric analysis was implemented for 2 independent groups. During the treatment course, the SD+ECT group showed a decreased seizure threshold, from 190.4 mC in the first ECT session to 176.4 mC in the last ECT session, whereas the ECT group showed an increased seizure threshold, increasing from 190.4 mC to 321.91 mC. Sleep deprivation is an effective and safe technique used to lower the seizure threshold of ECT and to obtain an adequate seizure time without increasing the energy applied.

Aged↗

PubMed2005

Exploratory analysis of longitudinal trials with staggered intervention times.

Longitudinal trials involving surgical interventions commonly have subject-specific intervention times, due to constraints on the availability of surgeons and operating theatres. Moreover, the intervention often effects a discontinuous change in the mean response. We propose a nonparametric estimator for the mean response profile of longitudinal data with staggered intervention times and a discontinuity at the times of intervention, as an exploratory tool to assist the formulation of a suitable parametric model. We use an adaptation of the standard generalized additive model algorithm for estimation, with smoothing constants chosen by a cross-validation criterion. We illustrate the method using longitudinal data from a trial to assess the effect of lung resection surgery in the treatment of emphysema patients.

Algorithms↗

PubMed2005

Pharmacodynamic analysis of the microbiological efficacy of telithromycin in patients with community-acquired pneumonia.

BACKGROUND AND OBJECTIVE: Telithromycin, a ketolide antibacterial, demonstrates concentration-dependent bactericidal activity against the major pathogens causing community-acquired respiratory tract infections. The objective of this study was to explore the relationships between pharmacokinetic/pharmacodynamic predictor variables, such as area under the plasma concentration-time curve (AUC) over minimum inhibitory concentration (MIC) [AUC/MIC], maximum plasma concentration (C(max)) over MIC (C(max)/MIC) and microbiological outcome from telithromycin therapy for community-acquired pneumonia (CAP). PATIENTS AND METHODS: Data were pooled from five phase III studies of oral telithromycin (800 mg once daily for 7-10 days) for the outpatient treatment of adults with CAP. Only subjects with a single pathogen isolated at baseline, a telithromycin MIC determination and at least one plasma pharmacokinetic sample were included. Bacteriologically modified intent-to-treat (bmITT) and bacteriologically evaluable per protocol (PPb) populations were analysed. Individual AUC and C(max) Bayesian estimates were obtained with a population pharmacokinetic model. Logistic regression, nonparametric smoothing, and classification analysis and regression tree (CART) were used to assess the relationship between AUC/MIC and C(max)/MIC and microbiological outcome by pathogen. RESULTS: The bmITT population included 224 patients (Streptococcus pneumoniae in 113, Haemophilus influenzae in 89 and Staphylococcus aureus in 22). Median telithromycin MIC was 0.015 microg/mL for S. pneumoniae, 2.0 microg/mL for H. influenzae and 0.12 microg/mL for S. aureus, with median AUC/MIC of 907.1, 6.9 and 98.4, and median C(max)/MIC of 172.0, 1.3 and 20.4 for the three pathogens, respectively. Both logistic regression and nonparametric smoothing showed the probability of microbiological cure to be consistently greater than 90% over the observed range of predictor variables. No reliable AUC/MIC or C(max)/MIC breakpoints were identified by CART. CONCLUSION: Telithromycin exhibits near-maximal efficacy against three major pathogens causing CAP at a dose of 800 mg once daily.

Adolescent↗

PubMed1997

Genomic survey of bipolar illness in the NIMH genetics initiative pedigrees: a preliminary report.

Four sites collaborated with the NIMH to develop a resource for the genetic study of bipolar (BP) illness. Common methods of ascertainment and assessment were developed in 1989. A series of families with a bipolar I (BPI) proband and at least one BPI or schizoaffective, bipolar type (SA/BP) first-degree relative has been studied. We now report initial data from a genomic survey with an average intermarker interval of 10 cM on 540 subjects from 97 families. This is the largest commonly ascertained and assessed linkage sample for bipolar illness reported to date; it includes 232 subjects with BPI, 32 SA/BP, 72 bipolar II (BPII), and 88 unipolar, recurrent (UPR). Nonparametric methods of analysis were employed, with all sites using affected sib pair analysis. The strongest findings thus far appear to be on chromosomes 1, 6, 7, 10, 16, and 22. Support has also been found for some previously reported linkages, including 21q and possibly Xq26. All these areas (as well as others) will be followed up with additional markers and further analyses. No locus tested thus far meets stringent criteria for an initial finding of significant linkage.

Alleles↗

PubMed2004

The dynamics of spatial behavior: how can robust smoothing techniques help?

A variety of setups and paradigms are used in the neurosciences for automatically tracking the location of an animal in an experiment and for extracting features of interest out of it. Many of these features, however, are critically sensitive to the unavoidable noise and artifacts of tracking. Here, we examine the relevant properties of several smoothing methods and suggest a combination of methods for retrieving locations and velocities and recognizing arrests from time series of coordinates of an animal's center of gravity. We accomplish these by using robust nonparametric methods, such as Running Median (RM) and locally weighted regression methods. The smoothed data may, subsequently, be segmented to obtain discrete behavioral units with proven ethological relevance. New parameters such as the length, duration, maximal speed, and acceleration of these units provide a wealth of measures for, e.g., mouse behavioral phenotyping, studies on spatial orientation in vertebrates and invertebrates, and studies on rodent hippocampal function. This methodology may have implications for many tests of spatial behavior.

Algorithms↗

PubMed2001

Elevated plasma surfactant protein-B predicts development of acute respiratory distress syndrome in patients with acute respiratory failure.

Surfactant protein-B is a lung specific protein secreted into the air spaces by pulmonary epithelial type II cells that leaks into the bloodstream in increased amounts in patients with ARDS. To test whether elevated plasma levels of surfactant protein-B would predict the development of ARDS in patients with acute hypoxemic respiratory failure, plasma and lung injury scores were collected at study entry and daily thereafter for 3 d from 54 patients admitted to our intensive care unit. ARDS was defined as a new bilateral infiltrate on chest radiograph and a lung injury score > or = 2.5. Twenty patients developed ARDS, of whom seven died. Although the initial lung injury score was not predictive of ARDS, the initial plasma surfactant protein-B was predictive (area under the curve = 0.77 [0.63 to 0.90], nonparametric receiver-operating characteristic analysis). In this cohort, plasma surfactant protein-B was particularly predictive of ARDS when applied to patients suffering a direct lung insult (area under the curve = 0.87 [0.72 to 1.02]), with a sensitivity of 85% (95% CI: 55 to 98%) and specificity of 78% (40 to 97%) at a cutoff of 4,994 ng/ml.

Acute Disease↗

PubMed2001

Nonparametric selection method of survival predictors with an application to breast cancer.

Mutual information between a survival variable and covariables provides a new tool for selecting covariables with a high predictive value whenever there is no reasonable parametric model with respect to the observed phenomena. The information rate carried out by covariables can be tested by means of a decomposition similar to the analysis of variance. Moreover, a method based on information conservation can be used for aggregating survival curves corresponding to different modalities of the same selected predictor which increases the prediction efficiency. These results are applied to survival data from 1304 patients with breast cancer followed over a period of ten years.

Breast Neoplasms↗

PubMed2001

A new prognosis factor analysis based on nonhomogeneous Markov description.

To evaluate prognosis factors, Cox's proportional hazard model has been used. But it was found that the analytical ability was not sufficient. So we propose a new evaluation method combining Markov chain model and multiple logistic regression analysis to estimate the prognosis factors. Stage II breast cancer was chosen as the subject. The data was retrospective data gathered in National Cancer Center Central Hospital. As first step, a simple Markov chain model was constructed to describe the state transition of a breast cancer. Then the multiple property of each state transition was investigated in detail. And the patients who had gotten a recurrence for the first two and a half years were discriminated as the poor prognosis group by a nonparametric test (p < 0.05). And the result proved to corresponding with the clinical experience. As second step, three factors (n classification of pathological diagnosis, ductal spread, and estrogen receptor) were selected as the prognosis factors for the early death in Stage II breast cancer by a multiple logistic regression analysis. This new prognosis factor analysis could find out some scientific evidences. Especially, it was found to be remarkable efficient in proving clinically experienced observation.

Breast Neoplasms↗

PubMed2002

Kernel estimates for one- and two-dimensional ion channel dwell-time densities.

In this paper, we compare nonparametric kernel estimates with smoothed histograms as methods for displaying logarithmically transformed dwell-time distributions. Kernel density plots provide a simpler means for producing estimates of the probability density function (pdf) and they have the advantage of being smoothed in a well-specified, carefully controlled manner. Smoothing is essential for multidimensional plots because, with realistic amounts of data, the number of counts per bin is small. Examples are presented for a 2-dimensional pdf and its associated dependency-difference plot that display the correlations between successive dwell times.

Ion Channels↗

PubMed2003

Partial AUC estimation and regression.

Accurate diagnosis of disease is a critical part of health care. New diagnostic and screening tests must be evaluated based on their abilities to discriminate diseased from nondiseased states. The partial area under the receiver operating characteristic (ROC) curve is a measure of diagnostic test accuracy. We present an interpretation of the partial area under the curve (AUC), which gives rise to a nonparametric estimator. This estimator is more robust than existing estimators, which make parametric assumptions. We show that the robustness is gained with only a moderate loss in efficiency. We describe a regression modeling framework for making inference about covariate effects on the partial AUC. Such models can refine knowledge about test accuracy. Model parameters can be estimated using binary regression methods. We use the regression framework to compare two prostate-specific antigen biomarkers and to evaluate the dependence of biomarker accuracy on the time prior to clinical diagnosis of prostate cancer.

Area Under Curve↗

PubMed2002

Sequential estimation in line transect surveys.

This article considers using sequential procedures to determine the amount of survey effort required in a line transect survey in order to achieve a certain precision level in estimating the abundance of a biological population. Sequential procedures are constructed for both parametric and nonparametric animal abundance estimators. The criterion used to derive the stopping rules is the width of confidence intervals for the animal abundance. For each estimator considered, we develop stopping rules based on the asymptotic distributions and the bootstrap. A sequential analysis on an aerial survey of the southern bluefin tuna indicates substantial saving of survey effort can be made by employment of the proposed sequential procedures. This savings of survey effort is also observed in a simulation study designed to evaluate the empirical performance of the proposed sequential procedures.

Animals↗

PubMed1994

Review of nonparametric methods for the analysis of crossover studies.

This paper reviews nonparametric methods for the analysis of crossover studies. Primary attention is given to crossover studies to compare two treatments for a response variable that has a metric measurement level. For this situation, one can often test hypotheses or obtain confidence intervals for parameters of interest by applying well known univariate nonparametric rank methods (e.g., the Wilcoxon rank sum test, or the Wilcoxon signed rank test) to appropriately specified functions of the data. Related extensions are also available, to some degree, for crossover studies to compare more than two treatments or those for which the measurement level of the response variable is ordinal or has a censored time-to-event nature. Methods for several specific situations along these lines are discussed in terms of principles with potentially broader applicability. Several examples are provided to illustrate the performance of some of the methods.

Confidence Intervals↗

PubMed2005

One- and two-sample nonparametric inference procedures in the presence of a mixture of independent and dependent censoring.

In survival analysis, the event time T is often subject to dependent censorship. Without assuming a parametric model between the failure and censoring times, the parameter Theta of interest, for example, the survival function of T, is generally not identifiable. On the other hand, the collection Omega of all attainable values for Theta may be well defined. In this article, we present nonparametric inference procedures for Omega in the presence of a mixture of dependent and independent censoring variables. By varying the criteria of classifying censoring to the dependent or independent category, our proposals can be quite useful for the so-called sensitivity analysis of censored failure times. The case that the failure time is subject to possibly dependent interval censorship is also discussed in this article. The new proposals are illustrated with data from two clinical studies on HIV-related diseases.

Anti-HIV Agents↗

PubMed2005

Estimating the species accumulation curve using mixtures.

As a significant tool in ecological studies, the species accumulation curve or the collector's curve is the graph of the expected number of detected species as a function of sampling effort. The problem of estimating the species accumulation curve based on an empirical data set arising from quadrat sampling is studied in a nonparametric binomial mixture model. It will be shown that estimating the species accumulation curve not only is independent of the unknown number of species but also includes estimating the number of species as a limiting case. For the purpose of interpolation, moment-based estimators, associated with asymptotic confidence intervals, are developed from several points of view. A likelihood-based procedure is developed for the purpose of extrapolation, associated with bootstrap confidence intervals. The proposed methods are illustrated by ecological data sets.

Animals↗

PubMed2005

Adjusting O'Brien's test to control type I error for the generalized nonparametric Behrens-Fisher problem.

O'Brien (1984, Biometrics 40, 1079-1087) introduced a simple nonparametric test procedure for testing whether multiple outcomes in one treatment group have consistently larger values than outcomes in the other treatment group. We first explore the theoretical properties of O'Brien's test. We then extend it to the general nonparametric Behrens-Fisher hypothesis problem when no assumption is made regarding the shape of the distributions. We provide conditions when O'Brien's test controls its error probability asymptotically and when it fails. We also provide adjusted tests when the conditions do not hold. Throughout this article, we do not assume that all outcomes are continuous. Simulations are performed to compare the adjusted tests to O'Brien's test. The difference is also illustrated using data from a Parkinson's disease clinical trial.

Algorithms↗