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PubMed1988

The statistical analysis of treatment effects in 24-hour ambulatory blood pressure recordings.

This paper presents a statistical analysis of treatment effects in 24-hour ambulatory blood pressure recordings. The statistical models account for circadian rhythms, subject effects, and the effects of treatment with drugs or relaxation therapy. In view of the heterogeneity of the subjects, we fit a separate linear model to the data of each subject, use robust statistical procedures to estimate the parameters of the linear models, and trim the data on a subject by subject basis. We use a meta-analytical method to combine the results of all subjects in the study.

Activity Cycles↗
PubMed1990

Statistical interim monitoring of the Cardiac Arrhythmia Suppression Trial.

The Cardiac Arrythmia Suppression Trial was stopped much earlier than planned. Statistical considerations played a very important role in the decision. Flexible group sequential testing was developed for the trial by implementing a Lan and DeMets procedure with use of the permutation test. We compute P-values from the joint permutation distribution of the test statistics, so we do not need to estimate the sampling distribution which in general is rather difficult to do without strict assumptions. The method also gives an exact test for small samples and allows us to use more complicated or non-Gaussian statistics. We also utilized stochastic curtailment ideas to evaluate various scenarios that might occur during the course of the trial, which assisted the Data and Safety Monitoring Board in making appropriate decisions.

Anti-Arrhythmia Agents↗
PubMedDate not supplied

The impact of the international guideline entitled Statistical Principles for Clinical Trials (ICH E9).

At the time of writing, the ICH E9 Note for Guidance entitled "Statistical principles for clinical trials" has been in force in Europe, Japan and the U.S.A. for almost a year. The purpose of this paper is to review the initial progress of E9 in terms of its degree of acceptance and also in terms of any early problems which have emerged. A different means of exploring these questions has been adopted in each of the three regions. From Europe there is a regulatory perspective on statistical issues which have been found to be incompletely covered within E9 and which have been important for specific regulatory decisions. From the U.S. there is a report of the results of a survey of U.S. pharmaceutical industry opinion concerning the effect of E9 on statistical practice in drug development. From Japan there is a discussion of the shortage of qualified statisticians in Japan and the difficulties that this causes when trying to implement E9. Some overall conclusions are drawn.

Clinical Trials as Topic↗
PubMed1999

The stationary statistical properties of human coding sequences.

We introduce a generally applicable method for the discovery and quantitation of all of the characteristic statistical properties of a class of biological sequences, given examples from the class. This method employs a reversible binary encoding of sequences into the binary digits -1 and +1. Then, provided that the sample is sufficient, the sample cumulants on the subsets of digit positions will manifest all of the statistical properties of the class. As an illustration, we present the main results of a complete characterization of the stationary statistical properties of human coding sequences, in terms of their sample cumulants. Many of the telling sample cumulants are described.

Base Sequence↗
PubMed1997

Empirical analyses of BOLD fMRI statistics. I. Spatially unsmoothed data collected under null-hypothesis conditions.

Temporal autocorrelation, spatial coherency, and their effects on voxel-wise parametric statistics were examined in BOLD fMRI null-hypothesis, or "noise," datasets. Seventeen normal, young subjects were scanned using BOLD fMRI while not performing any time-locked experimental behavior. Temporal autocorrelation in these datasets was described well by a 1/frequency relationship. Voxel-wise statistical analysis of these noise datasets which assumed independence (i.e., ignored temporal autocorrelation) rejected the null hypothesis at a higher rate than specified by the nominal alpha. Temporal smoothing in conjunction with the use of a modified general linear model (Worsley and Friston, 1995, NeuroImage 2: 173-182) brought the false-positive rate closer to the nominal alpha. It was also found that the noise fMRI datasets contain spatially coherent time signals. This observed spatial coherence could not be fully explained by a continuously differentiable spatial autocovariance function and was much greater for lower temporal frequencies. Its presence made voxel-wise test statistics in a given noise dataset dependent, and thus shifted their distributions to the right or left of 0. Inclusion of a "global signal" covariate in the general linear model reduced this dependence and consequently stabilized (i.e., reduced the variance of) dataset false-positive rates.

Artifacts↗
PubMed1998

Mapping voxel-based statistical power on parametric images.

Using a classic technique based on the noncentral F-distribution method for computing statistical power, we developed a general approach to the estimation of voxel-based power in functional brain image data analysis. We applied this method to PET data from a large sample (N = 40) of subjects performing the Wisconsin Card Sorting (WCST) paradigm analyzed with SPM95, produced statistical power maps for a range of samples sizes and smoothing filter widths, and examined the effects of sample size and image smoothing on the expected reliability of activation findings. At an uncorrected alpha of 0.01, a fixed filter size of 10 mm3, and a range of power thresholds, maps revealed that the power to reject the null hypothesis in brain regions implicated in the task at Ns of 5 and 10 may not be sufficient to ensure reliable replication of significant findings and so should be interpreted with caution. At sample sizes approaching 20 subjects, sufficient power was found in the right dorsolateral prefrontal cortex (BA 46/9), right and left inferior parietal lobule (BA 40), and left inferior temporal lobe (BA 37), comprising the cortical network typically observed during the WCST. Filter size needed to maximize power varied widely, but systematically, across the brain, tending to follow known neuroanatomical landmarks. Statistical power considerations in brain imaging studies are critical for controlling the rate of false negatives and assuring reliable detection of cognitive activation. The variation of filter size for maximizing power across the brain suggests that the underlying neuroanatomy of functional units is an important consideration in the a priori selection of filter size.

Algorithms↗
PubMed2002

Combining brains: a survey of methods for statistical pooling of information.

More than one subject is scanned in a typical functional brain imaging experiment. How can the scientist make best use of the acquired data to map the specific areas of the brain that become active during the performance of different tasks? It is clear that we can gain both scientific and statistical power by pooling the images from multiple subjects; furthermore, for the comparison of groups of subjects (clinical patients vs healthy controls, children of different ages, left-handed people vs right-handed people, as just some examples), it is essential to have a "group map" to represent each population and to form the basis of a statistical test. While the importance of combining images for these purposes has been recognized, there has not been an organized attempt on the part of neuroscientists to understand the different statistical approaches to this problem, which have various strengths and weaknesses. In this paper we review some popular methods for combining information, and demonstrate the surveyed techniques on a sample data set. Given a combination of brain images, the researcher needs to interpret the result and decide on areas of activation; the question of thresholding is critical here and is also explored.

Adult↗
PubMed2001

Exponential distance statistics to detect the effects of population subdivision.

Statistical tests are needed to determine whether spatial structure has had a significant effect on the genetic differentiation of subpopulations. Here we introduce a new family of statistics based on a sum of an exponential function of the distances between individuals, which can be used with any genetic distance (e.g., nucleotide differences, number of nonshared alleles, or separation on a phylogenetic tree). The power of the tests to detect genetic differentiation in Wright-Fisher island models and stepping stone models was calculated for various sample sizes, rates of migration and mutation, and definitions of spatial neighborhoods. We found that our new test was in some cases more powerful than the Ks* statistic of Hudson et al. (Mol. Biol. Evol. 9, 138-151, 1992), but in all cases was slightly less powerful than both a traditional chi2 test without lumping of rare haplotypes and the S(nn) test of Hudson (Genetics 155, 2011-2014, 2000). However, when we applied our new tests to three data sets, we found in some cases highly significant results that were missed by the other tests.

Animals↗
PubMed1984

Guidelines for the statistical evaluation of SCE.

When planning studies by the sister chromatid exchange (SCE) test, it is necessary to calculate the size of the test groups, taking into consideration the variance of the test result and the statistical distribution of SCE frequencies. This paper deals with these problems. Recommendations are given for the preparation of slides under standardized conditions, for the subsequent counting of SCEs/cell in a random sample of 30 cells from each slide, and for the condensation of the information contained in the sample of 30 counts into a single statistic, that may be treated as a normally distributed variable. The adequacy of this transformation is shown for the data from 170 different subjects. Of these, 165 (58 nonsmokers and 107 cigarette smokers) had mean values of SCE/cell ranging from 6.5 to 13.5, while the remaining 5 subjects were on intermittent treatment with cytostatics every fourth wk, and exhibited a mean value of SCE/cell in the range 15-23. The variance associated with the recommended statistic has been decomposed into 4 variance components: variance within slides, variance between slides prepared from the same blood sample, variance within subjects, and variance between subjects. Based on a total of 680 SCE analyses in 218 persons, estimates of these variance components are given and used to calculate the necessary number of samples for the detection of a prescribed difference in SCEs/cell for selected values of Type I and Type II errors.

Analysis of Variance↗
PubMed2003

Permutation tests for classification: towards statistical significance in image-based studies.

Estimating statistical significance of detected differences between two groups of medical scans is a challenging problem due to the high dimensionality of the data and the relatively small number of training examples. In this paper, we demonstrate a non-parametric technique for estimation of statistical significance in the context of discriminative analysis (i.e., training a classifier function to label new examples into one of two groups). Our approach adopts permutation tests, first developed in classical statistics for hypothesis testing, to estimate how likely we are to obtain the observed classification performance, as measured by testing on a hold-out set or cross-validation, by chance. We demonstrate the method on examples of both structural and functional neuroimaging studies.

Algorithms↗
PubMed2003

Construction of a statistical model for cardiac motion analysis using nonrigid image registration.

In this paper we present a new technique for tracking the movement of the myocardium using a statistical model derived from the motion fields in the hearts of several healthy volunteers. To build the statistical model we tracked the motion of the myocardium in 17 volunteers using a nonrigid registration technique based on free-form deformations and mapped the motion fields obtained into a common reference coordinate system. A principal component analysis (PCA) was then performed on the motion fields to extract the major modes of variation in the fields between the successive time frames. The modes of variation obtained were then used to parametrize the free-form deformations and build our statistical model. The results of using our model to track the motion of the heart in normal volunteers are also presented.

Algorithms↗
PubMed1993

Statistical tests of models of DNA substitution.

Penny et al. have written that "The most fundamental criterion for a scientific method is that the data must, in principle, be able to reject the model. Hardly any [phylogenetic] tree-reconstruction methods meet this simple requirement." The ability to reject models is of such great importance because the results of all phylogenetic analyses depend on their underlying models--to have confidence in the inferences, it is necessary to have confidence in the models. In this paper, a test statistic suggested by Cox is employed to test the adequacy of some statistical models of DNA sequence evolution used in the phylogenetic inference method introduced by Felsenstein. Monte Carlo simulations are used to assess significance levels. The resulting statistical tests provide an objective and very general assessment of all the components of a DNA substitution model; more specific versions of the test are devised to test individual components of a model. In all cases, the new analyses have the additional advantage that values of phylogenetic parameters do not have to be assumed in order to perform the tests.

Animals↗
PubMed1990

A note on the statistical properties of animal locations.

A statistical model of the successive locations of an animal in the plane induces a statistical model of the relative positions of successive locations. A common locational model is that the Cartesian coordinates of successive locations in the plane are independent bivariate normal random variables. This note gives the statistical properties of the direction and length of the vector joining successive locations.

Animals↗
PubMed1993

Simple diagnostic statistical tests of models for DNA substitution.

The accuracy of models for DNA substitution used in phylogenetic analyses is becoming more important with the increasing availability and analysis of molecular sequence data. It is natural to look for ways of improving these models, and to do this in a planned manner it is useful to be able to identify features of sequences that may not be described adequately. In this paper, I describe three statistics which may give useful diagnostic information on departures from models' predictions. The statistical distributions of these statistics are discussed and simple significance tests are derived. These tests are based on the (estimated) phylogeny of the sequences and so have the advantage of using the information contained in this tree. Examples are given of the application of the new tests to Markov chain models describing the evolution of primate pseudogene sequences and small-subunit RNA sequences.

Animals↗
PubMed1984

Collective properties of neural networks: a statistical physics approach.

Among the various models proposed so far to account for the properties of neural networks, the one devised by Little and the one derived by Hopfield prove to be the most interesting because they allow the use of statistical mechanics techniques. The link between the Hopfield model and the statistical mechanics is provided by the existence of an extensive quantity. When the synaptic plasticity behaves according to a Hebbian procedure, the analogy with the classical spin glass models studied by Van Hemmen is complete. In particular exact solutions describing the steady states of noisy systems are found. On the other hand, the Little model introduces a Markovian dynamics. One shows that the evolution equation obeys the microreversibility principle if the synaptic efficiencies are symmetrical. Therefore, assuming that such a symmetry materializes, the Little model has to obey a Gibbs statistics. The corresponding Hamiltonian is derived accordingly. At last, using these results, both models are shown to display associative memory properties. In particular the storage capacity of neural networks working along with the Little dynamics is similar to the capacity of Hopfield neural networks. The conclusion drawn from the study of the Hopfield model can be extended to the Little model, which is certainly a more realistic description of the biological situation.

Action Potentials↗
PubMed1975

[Morphology versus prognosis in renal cell carcinoma a statistical approach].

In a group of 102 selected cases of renal cell carcinoma which at various periods after nephrectomy terminated fatally, age, sex, and 23 gross and/or histologic tumor characteristics were examined, subclassified, and evaluated. An attempt was made to correlate these parameters statistically to postoperative survival time. A newly developed and programmed statistical method, i.c. "dichotomic variance analysis", proved to be superior to both multiple regression and cluster analysis. Using infiltrative-destructive tumor growth, polymorphy, and chromatin density of tumor cell nuclei, extension of renal vein invasion, age and sex, as the only 6 required out of 25 distinguished tumor parameters, this statistical multivariate method comprised 7 distinctive groups of different mean geometrical postoperative survival time, obviously corresponding to 7 tumor types of increasing degree of malignancy. By step-wise dichotomic splitting of tumor groups it therefore was possible to delinate schematically some of the complex connections between the criteria or variables of prognostic significance. Conceivable sources of errors possibly influencing reproducibility and practical applicability of the presented dichotomic variance analysis in evaluating prognostic criteria in renal cell carcinoma are discussed.

Adult↗
PubMed1986

A method linking statistics and knowledge engineering for making medical consulting systems. A medical consulting system for electric response audiometry through auditory slow vertex response.

There are two methods of making medical consulting systems: the statistical method and the knowledge engineering method. Since both of these methods seem to be very different from each other, they have been recognized and applied separately. We contend, however, that a combination of statistics and knowledge engineering is a more effective and suitable way to create a medical consulting system than is the use of either method alone. In order to justify this contention, we created a medical consulting system, AUTSVR-V1.1, which detects auditory slow vertex responses (SVR) through observing and identifying background activities of the electroencephalogram (EEG) automatically during measurement of SVRs for the purpose of objective electric response audiometry (ERA), and compared it with AUTSVR-V1.0, which depends on statistics only.

Audiometry, Evoked Response↗