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PubMed2002

Statistical parametric mapping of LORETA using high density EEG and individual MRI: application to mismatch negativities in schizophrenia.

We describe a method for the statistical parametric mapping of low resolution electromagnetic tomography (LORETA) using high-density electroencephalography (EEG) and individual magnetic resonance images (MRI) to investigate the characteristics of the mismatch negativity (MMN) generators in schizophrenia. LORETA, using a realistic head model of the boundary element method derived from the individual anatomy, estimated the current density maps from the scalp topography of the 128-channel EEG. From the current density maps that covered the whole cortical gray matter (up to 20,000 points), volumetric current density images were reconstructed. Intensity normalization of the smoothed current density images was used to reduce the confounding effect of subject specific global activity. After transforming each image into a standard stereotaxic space, we carried out statistical parametric mapping of the normalized current density images. We applied this method to the source localization of MMN in schizophrenia. The MMN generators, produced by a deviant tone of 1,200 Hz (5% of 1,600 trials) under the standard tone of 1,000 Hz, 80 dB binaural stimuli with 300 msec of inter-stimulus interval, were measured in 14 right-handed schizophrenic subjects and 14 age-, gender-, and handedness-matched controls. We found that the schizophrenic group exhibited significant current density reductions of MMN in the left superior temporal gyrus and the left inferior parietal gyrus (P < 0. 0005). This study is the first voxel-by-voxel statistical mapping of current density using individual MRI and high-density EEG.

Adolescent↗
PubMed2002

Statistical determination of cost-effectiveness frontier based on net health benefits.

Statistical methods are given for producing a cost-effectiveness frontier for an arbitrary number of programs. In the deterministic case, the net health benefit (NHB) decision rule is optimal; the rule funds the program with the largest positive NHB at each lambda, the amount a decision-maker is willing to pay for an additional unit of effectiveness. For bivariate normally distributed cost and effectiveness variables and a specified lambda, a statistical procedure is presented, based on the method of constrained multiple comparisons with the best (CMCB), for determining the program with the largest NHB. A one-tailed t test is used to determine if the NHB is positive. To obtain a statistical frontier in the lambda-NHB plane, we develop a method to produce the region in which each program has the largest NHB, by pivoting a CMCB confidence interval. A one-sided version of Fieller's theorem is used to determine the region where the NHB of each program is positive. At each lambda, the pointwise error rate is bounded by a prespecified alpha. Upper bounds on the familywise error rate, the probability of an error at any value of lambda, are given. The methods are applied to a hypothetical clinical trial of antipsychotic agents.

Algorithms↗
PubMed2005

Statistical correlation between cell adhesion and proliferation on biocompatible metallic materials.

Our ambition for several years is to appreciate and quantify the long-term adhesion of cells on materials at times where the interface between cells and substrate becomes more complex, more closed to the cell/matrix/substrate interface existing in vivo. With this objective, we quantified the long-term adhesion and proliferation of human osteoblasts cultured from 24 h to 21 days on pure titanium, titanium alloy, and stainless-steel substrates presenting six different surface morphologies and two different roughness amplitude. Hence, we did proceed to the statistical correlation of cell adhesion and cell proliferation on 30 different substrates. Additionally, we described surface topography not only by the roughness amplitude but also by the roughness morphology using new specific parameters. By multiple analysis of variance, we demonstrated that nor material composition nor surface roughness amplitude did influence cell proliferation, whereas a very significant influence of the process used to produce the surface was observed meaning that the main influent factor on cell proliferation was the surface morphology. The long-term adhesion and proliferation capacity of cells were positively correlated on 23 types of substrates on 30, this positive correlation being statistically asserted on 13 types of substrates on 23. This study is the first demonstration of the existence of a statistical correlation between long-term adhesion and proliferation capacity of human bone cells on substrates with various chemical composition, surface chemistry, and surface topography.

Biocompatible Materials↗
PubMed1993

A novel statistical approach for the comparison of analytical methods to measure angiotensin converting enzyme activity, enalaprilat, and benazeprilat.

Two different analytical techniques were used to measure angiotensin converting enzyme (ACE) activity, and three different methods were used to measure each of the ACE inhibitors enalaprilat and benazeprilat. All measurements were made in human plasma. The groups of methods were compared by two different statistical approaches. First, the means of the methods were compared by the paired t test or analysis of variance, depending on whether two or three different methods were under comparison. Second, the squared coefficients of variation of the methods were compared by the Jackknife technique. The dual statistical approach employed enabled both the accuracy and the variability of the analytical methods to be compared and is a superior approach to the inappropriate use of correlation coefficients that are commonly used to compare analytical techniques. No statistically significant difference was found between the two assays used to measure ACE activity. Differences were found between the three methods to measure enalaprilat, although no obvious reason could be found for this phenomenon. Significant differences were also found between the three methods used to measure benazeprilat and were attributed to the presence of metabolites interfering in the nonspecific assay methods.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1997

Estimating test-retest reliability in functional MR imaging. I: Statistical methodology.

A common problem in the analysis of functional magnetic resonance imaging (fMRI) data is quantifying the statistical reliability of an estimated activation map. While visual comparison of the classified active regions across replications of an experiment can sometimes by informative, it is typically difficult to draw firm conclusions by inspection; noise and complex patterns in the estimated map make it easy to be misled. Here, several statistical models, of increasing complexity, are developed, under which "test-retest" reliability can be meaningfully defined and quantified. The method yields global measures of reliability that apply uniformly to a specified set of brain voxels. The estimates of these reliability measures and their associated uncertainties under these models can be used to compare statistical methods, to set thresholds for detecting activation, and to optimize the number of images that need to be acquired during an experiment.

Brain↗
PubMed2003

Effect of changing data collection parameters on statistical motor unit number estimates.

The effect of number of samples and selection of data for analysis on the calculation of surface motor unit potential (SMUP) size in the statistical method of motor unit number estimates (MUNE) was determined in 10 normal subjects and 10 with amyotrophic lateral sclerosis (ALS). We recorded 500 sequential compound muscle action potentials (CMAPs) at three different stable stimulus intensities (10-50% of maximal CMAP). Estimated mean SMUP sizes were calculated using Poisson statistical assumptions from the variance of 500 sequential CMAP obtained at each stimulus intensity. The results with the 500 data points were compared with smaller subsets from the same data set. The results using a range of 50-80% of the 500 data points were compared with the full 500. The effect of restricting analysis to data between 5-20% of the CMAP and to standard deviation limits was also assessed. No differences in mean SMUP size were found with stimulus intensity or use of different ranges of data. Consistency was improved with a greater sample number. Data within 5% of CMAP size gave both increased consistency and reduced mean SMUP size in many subjects, but excluded valid responses present at that stimulus intensity. These changes were more prominent in ALS patients in whom the presence of isolated SMUP responses was a striking difference from normal subjects. Noise, spurious data, and large SMUP limited the Poisson assumptions. When these factors are considered, consistent statistical MUNE can be calculated from a continuous sequence of data points. A 2 to 2.5 SD or 10% window are reasonable methods of limiting data for analysis.

Action Potentials↗
PubMed2003

Statistical motor unit number estimation: from theory to practice.

Statistical motor unit number estimation (MUNE) is one of several experimental techniques used to estimate the number of lower motor neurons innervating a given muscle. All are fairly reproducible and have been applied successfully in monitoring neurogenic disease progression. Quantitating the number of lower motor neurons is important, since the compound muscle action potential (CMAP) and strength may not change as rapidly over time due to the confounding effect of reinnervation. MUNE techniques differ in the way they obtain samples of surface-recorded motor unit potentials (SMUP). Statistical MUNE is based on Poisson statistics, uses surface stimulation, and is useful in testing distal, superficial nerves. This review focuses on the theory behind the development of the technique, critiques the publications resulting from applying the technique in control and disease subjects, and discusses the future developments needed for clinical utility.

Action Potentials↗
PubMed2005

Epidemiologic studies of adverse effects of anti-retroviral drugs: how well is statistical power reported.

PURPOSE: To determine whether there is a difference in average statistical power between pharmacoepidemiologic studies of anti-retroviral adverse drug effects (ADEs) sponsored by for-profit versus non-profit organizations. METHODS: We studied all published pharmacoepidemiologic studies of ADEs associated with the 15 anti-retroviral drugs approved through the end of 1999. A priori, the primary outcome was the power of each study to detect a clinically important difference in the risk for an adverse effect among patients exposed to the study drug(s). We could not evaluate this outcome because of the infrequent reporting of power calculations. We instead report the distribution of studies across a 5-tiered measure of adequacy of reporting of statistical power, as well as the sponsorship of these studies. RESULTS: Of 48 studies meeting our inclusion criteria, only 1 (2%) reported either a completed, a priori power calculation or sufficient details for readers to calculate the power to detect a pre-defined, clinically important effect. Thirty-five studies (73%) reported the minimum information required for sophisticated readers to determine the power to detect an event rate of interest to them; 6 additional studies (13%) reported confidence intervals around at least one summary effect measure and 6 (13%) provided no indication of power or uncertainty. Of the 41 studies for which sponsorship was determined, only 3 (7%) were sponsored by for-profit organizations. CONCLUSIONS: The poor reporting of statistical power in this sample suggests a need for guidelines to improve the reporting of pharmacoepidemiologic studies of ADEs. Future research is needed to determine whether the observed paucity of industry-sponsored observational studies of anti-retroviral ADEs extends to other clinical areas, and if so, to identify the causes of this phenomenon.

Adverse Drug Reaction Reporting Systems↗
PubMed2006

Improvement of statistical potentials and threading score functions using information maximization.

We show that statistical potentials and threading score functions, derived from finite data sets, are informatic functions, and that their performance depends on the manner in which data are classified and compressed. The choice of sequence and structural parameters affects estimates of the conditional probabilities P(C|S), the quantification of the effect of sequence S on conformation C, and determines the amount of information extracted from the data set, as measured by information gain. The mathematical link between information gain and mean conformational energy, established in this work using the local backbone potential as model, demonstrates that manipulation of descriptive parameters also alters the "energy" values assigned to native conformation and to decoy structures in the test pool, and consequently, the performance of such statistical potential functions in fold recognition exercises. We show that sequence and structural partitions that maximize information gain also minimize the mean energy of the ensemble of native conformations. Moreover, we establish an informatic basis for the placement of the native score within an energy spectrum given by the decoy pool in a threading exercise. We discover that, among all informatic quantities, information gain is the best predictor of threading success, even better than the standard Z-score. Consequently, the choices of sequence and structural descriptors, extent of compression, and levels of discretization that maximize information gain must also produce the best potential functions. Strategies to optimize these parameters with respect to information extraction are therefore relevant to building better statistical potentials. Last, we demonstrate that the backbone torsion potential, defined by the trimer sequence, can be an effective tool in greatly reducing the set of possible conformations from a vast decoy pool.

Amino Acid Sequence↗
PubMed2005

Multidimensional statistical analysis applied to electron ionization mass spectra to determine steroid stereochemistry.

The differentiation of stereoisomers on the basis of their mass spectra only is usually a difficult challenge even when an informative ionization technique such as electron ionization is used; this is particularly the case for steroids. In this study, multivariate statistical techniques have been applied to the mass spectra of derivatized 5xi-androstane-3xi,17xi-diols (xi = alpha,beta) in order to investigate the possibility of discrimination among the different isomers. After collection of the data from the mass spectra (20 replicates for each of the 8 isomers), each ion was considered as a statistical variable and each mass spectrum as an observation. The more discriminative variables (42 out of the 160 initial ones) were selected using the analysis of variance technique (ANOVA). Thereafter, a linear discriminant analysis (LDA) allowed us to set up a predictive model for stereochemistry determination. The two-dimensional graphical display of the 160 observations on the basis of the canonical variables derived from LDA made it possible to separate the eight isomers. The discrimination of 5alpha and 5beta isomers as well as 3alpha and 3beta was unambiguous, whereas, the discrimination of 17alpha and 17beta epimers was less obvious. The robustness of the model was checked with 40 mass spectra recorded over a 6-month period on different quadrupole mass spectrometers and under different signal acquisition conditions. The percentage of correct assignment of these 'unknown' stereoisomers was 92%; only three 17alpha and 17beta epimers were not correctly plotted in the expected zone. Nevertheless, the performance score was better than those observed with traditional mass spectral libraries. Furthermore, this statistical approach allowed us to identify the main fragment ions involved in the discrimination between isomers: m/z 256 and 421 for isomers 5a-5b; m/z 241 and 331 for isomers 5alpha3alpha-5alpha3beta; m/z 143 and 162 for isomers 5beta3alpha-5beta3beta; and m/z 255 for epimers 17alpha-17beta.

Androstenediols↗
PubMed2002

Inflation of type I error rate in two statistical tests for the detection of publication bias in meta-analyses with binary outcomes.

The use of meta-analysis to combine results of several trials is still increasing in the medical field. The validity of a meta-analysis may be affected by various sources of bias (for example, publication bias, language bias). Therefore, an analysis of bias should be an integral part of any systematic review. Statistical tests and graphical methods have been developed for this purpose. In this paper, two statistical tests for the detection of bias in meta-analysis were investigated in a simulation study. Binary outcome data, which are very common in medical applications, were considered and relative effect measures (odds ratios, relative risk) were used for pooling. Sample sizes were generated according to findings in a survey of eight German medical journals. Simulation results indicate an inflation of type I error rates for both tests when the data are sparse. Results get worse with increasing treatment effect and number of trials combined. Valid statistical tests for the detection of bias in meta-analysis with sparse data need to be developed.

Computer Simulation↗
PubMed2004

A general statistical principle for changing a design any time during the course of a trial.

A general method is presented that allows the researcher to change statistical design elements such as the residual sample size during the course of an experiment, to include an interim analysis for early stopping when no formal rule for early stopping was foreseen, to increase or reduce the number of planned interim analyses, to change time points and the type I error spending function for the further design of interim analyses, or to change the test statistic, the outcome measure, etc. At the time of a pre-planned interim analysis for early stopping or at any time of an interim look without spending part of the type I error level the method offers the option to completely redesign the remaining part of the trial, without affecting the type I error level. The method is described in the usual Brownian motion model and extended to the general context of statistical decision functions. It is based on the conditional rejection probability of a decision variable.

Antiparkinson Agents↗
PubMed2006

On non-inferiority margin and statistical tests in active control trials.

The problem of selecting a non-inferiority margin and the corresponding statistical test for non-inferiority in active control trials is considered. For selection of non-inferiority margin, the guideline by the International Conference on Harmonization (ICH) recommends that the non-inferiority margin should be chosen in such a way that if the non-inferiority of the test therapy to the active control agent is claimed, the test therapy is not only non-inferior to the active control agent, but also superior to the placebo. Furthermore, variability should be taken into account. Along this line, a method for selecting non-inferiority margins with some statistical justification is proposed. Statistical tests for non-inferiority designed in the situation where the non-inferiority margin is an unknown parameter are derived. An example concerning a cancer trail for testing non-inferiority with the primary study endpoint of the time to disease progression is presented to illustrate the proposed method.

Antineoplastic Agents↗
PubMed2006

Temporal surveillance using scan statistics.

We describe two classes of statistics for testing an arbitrary model of disease incidence over time against an alternative model involving a spike (pulse) superimposed on this background. The statistics are each based on taking the maximum of some function comparing observed and expected numbers of events in a window of width w. One approach applies p-values for scan statistics calculated for a constant background rate to this more general problem. For a fixed window, w, the approach gives a simple formula to determine p-values for retrospective analysis, or to sound an alarm for either continuous or grouped prospective data. The latter application involves a new approximation for the distribution of the maximum number of cases in w consecutive intervals. The second approach based on generalized likelihood ratio tests (GLRTs), sounds an alarm for a higher than anticipated rate of events in a scanning window of fixed length, or for window sizes that lie in a region. GLRTs are constructed for continuous observations, for grouped data, or for a sequence of trials. As for GLRTs used in retrospective evaluations, simulation is required to implement the prospective procedure. For grouped surveillance data, we compare by simulation, operating characteristics of the P-scan with fixed windows (both correctly specified and not), the fixed-window GLRT, the variable-window GLRT, and a variant of the CUSUM. The simulations demonstrate a very high correlation between the P-scan and corresponding fixed-window GLRT.

Adult↗
PubMed2006

Statistical evaluation of biomarkers as surrogate endpoints: a literature review.

A valid surrogate endpoint allows correct inference to be drawn regarding the effect of an intervention on the unobserved true clinical endpoint of interest. The perceived practical and ethical advantages of substituting a surrogate endpoint for a clinical endpoint have led to a considerable number of statistical methods being proposed for the evaluation of a biomarker as a surrogate endpoint. We review the main statistical schools of thought which have developed and consider how the validation process might be arranged within the regulatory and practical constraints of the drug development process. We conclude by assessing which of the candidate statistical methods offer the best approach for surrogate endpoint evaluation.

Biomarkers↗
PubMed2006

An elliptic spatial scan statistic.

The spatial scan statistic is commonly used for geographical disease cluster detection, cluster evaluation and disease surveillance. The most commonly used shape of the scanning window is circular. In this paper we explore an elliptic version of the spatial scan statistic, using a scanning window of variable location, shape (eccentricity), angle and size, and with and without an eccentricity penalty. The method is applied to breast cancer mortality data from Northeastern United States and female oral cancer mortality in the United States. Power comparisons are made with the circular scan statistic.

Adolescent↗
PubMedDate not supplied

Mantel-Haenszel statistics and direct standardization.

This paper demonstrates that the Mantel-Haenszel chi-square statistic may be employed to test the equality of two directly standardized rates. For certain epidemiological applications, this eliminates the need for special computer programs to contrast two directly standardized rates. Furthermore, since the weights are determined entirely by the data there is the advantage of avoiding the selection of an external standard population. Data analysts who compare two groups of rates with the Mantel-Haenszel chi-square statistic may view this statistic as a comparative measure of two directly adjusted rates.

Age Factors↗