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PubMed2003

A subspace identification extension to the phase correlation method.

The phase correlation method (PCM) is known to provide straightforward estimation of rigid translational motion between two images. It is often claimed that the original method is best suited to identify integer pixel displacements, which has prompted the development of numerous subpixel displacement identification methods. However, the fact that the phase correlation matrix is rank one for a noise-free rigid translation model is often overlooked. This property leads to the low complexity subspace identification technique presented here. The combination of non-integer pixel displacement identification without interpolation, robustness to noise, and limited computational complexity make this approach a very attractive extension of the PCM. In addition, this approach is shown to be complementary with other subpixel phase correlation based techniques.

Algorithms↗

PubMed1996

Test of linear trend in eigenvalues of a covariance matrix with application to data analysis.

Principal component analysis and factor analysis are the most widely used tools for dimension reduction in data analysis. Both methods require some good criterion to judge the number of dimensions to be kept. The classical method focuses on testing the equality of eigenvalues. As real data hardly have this property, practitioners turn to some ad hoc criterion in judging the dimensionality of their data. One such popular method, the 'scree test' or 'scree plot' as described in many texts and statistical programs, is based on the trend in eigenvalues of sample covariance (correlation) matrix. The principal components or common factors corresponding to eigenvalues which exhibit a slow linear decrease are discarded in further data analysis. This paper develops a formal statistical test for the 'scree plot'. A special case of this test is the classical test for equality of eigenvalues which has been suggested in several texts as the criterion to decide the number of principal components to retain. Comparisons between equality of eigenvalues and the slow linear decrease in eigenvalues on some classical examples support the hypothesis of slow linear decrease. A physical background to such a phenomenon is also suggested.

Analysis of Variance↗

PubMed1999

Motor coordination in a multi-muscle system as revealed by principal components analysis of electromyographic variation.

The variation in electromyographic output of twelve trigeminal muscles of the rabbit was studied to test the hypothesis that they are under the control of a small number of independent neural factors. Jaw muscle electromyograms (EMGs) of eight animals were recorded in 95 chewing sequences, each consisting of 40-75 chewing cycles. The within-sequence correlations of the EMG burst amplitudes (integrated per cycle) and burst onsets were calculated between the muscles. The correlation matrix was subjected to a principal components analysis. This method aims at describing the variation in EMG amplitude and timing by means of the smallest possible set of newly defined variables, or principal components. Of the variation in EMG amplitude values of the twelve muscles, 75-90% could be accounted for by only three principal components. Each principal component was characterized by a group of muscles with high mutual positive correlations; they had zero correlation with other principal components. The first component represents the jaw closers: most of the bilateral masseter and the medial pterygoid muscles. The second represents the openers: the bilateral digastric and lateral pterygoid muscles. This demonstrates the tight control of both the jaw openers and closers, each by a single neural factor; these two factors are independent of one another. They most likely originate from the specific inputs from primary afferents to the opener and closer motoneurons. Unexpectedly, a third independent principal component appeared to control the closing activity of the non-chewing side, posterior deep masseter muscle. It was hypothesized that this muscle acts independently of the other closers to disengage the teeth and resets the jaw for a new chewing cycle. Principal components analysis of variation in timing of EMG onset revealed a grouping of all masticatory muscles in a single cluster, independent of EMG amplitude. This supports the hypothesis that timing and amplitude of masticatory EMG patterns are controlled independently.

Animals↗

PubMed1996

Effect of weather conditions on the flight activity of Nigerian blackflies (Diptera:Simuliidae).

A vehicle-mounted net was used to make hourly catches of blackflies at 700-1000 m altitude in the River Assob valley, central Nigeria, on 20 days during the dry season. Pearson Correlation Matrix analysis of the collection data and meteorology showed that the main factors affecting flight activity of each of the four most abundant blackfly species were primarily light intensity and secondly wind velocity, whereas relative humidity was the least important factor. Flight activity showed a negative linear regression against wind, with some activity occurring in wind speeds up to 15 km/h. Distance-weighted least-squares (DWLS) regressions showed little correlation of temperature with activity for Simulium hargreavesi and S.adersi, but S.squamosum and S.vorax had small peaks at 28 degrees C and 31 degrees C, respectively. DWLS regression against light intensity showed an activity peak at 6000 lux, except in Simulium adersi.

Animals↗

PubMed1999

Retinoic acid stimulates meningioma cell adhesion to the extracellular matrix and inhibits invasion.

Meningiomas are tumours derived from the arachnoid and pia mater. During embryogenesis, these membranes develop from the migrating craniofacial neural crest. We have previously demonstrated that meningiomas have characteristic features of embryonic meninges. Craniofacial neural crest derivatives are affected during normal development and migration by retinoic acid. We speculated, therefore, that meningioma cell migration and invasion would be affected in a similar way. In this study we investigated the mechanisms of invasion and migration in meningiomas and the effects of retinoic acid (RA). We found that low doses of RA inhibit in vitro invasion in meningioma cells, without affecting cell proliferation or viability. The matrix metalloproteinases MMP-2 (72 kDa gelatinase) and MMP-9 (92 kDa gelatinase), which play a key role in invasion in other tumours, are not affected by RA. RA inhibits cell migration on collagen I and fibronectin. A possible mechanism for these effects is provided by the fact that RA strongly stimulates adhesion of meningioma cells to extracellular matrix substrates. As in vitro invasion, migration and decreased adhesion to the extracellular matrix correlate with the clinical manifestation of tumour invasion, we conclude that RA induces a non-invasive phenotype in meningioma cells.

Cell Adhesion↗

PubMed1987

[Clinico-immunologic correlations in schizophrenia of various courses (on a B-lymphocyte model)].

The authors studied the relationship between the clinical parameters of schizophrenia and the immunological parameters as exemplified by the B-system of immunity. An analysis was conducted with the use of linear correlation coefficients whose sum (a correlational matrix) was subjected to a cluster analysis. The data obtained indicate a considerable increase in both levels and activity of B-lymphocytes in schizophrenic patients in an acute psychotic state. The characteristics of slowly-progressive schizophrenia distinguished by a torpid relatively benign course and mild mental disturbances also appear to determine a relatively mild nature of aberrations in the immunological status of the patients. The studied immunological parameters were found to correlate with the patients' age at the onset of the disease and at the time of psychosis manifestations. The authors supposed that the immunologic characteristics definitely correlated with the severity of the disease exacerbation, form, and gravity, while the degree of deviation of immunologic parameters from the norm makes it possible to better assess the nature of psychopathologic manifestations in schizophrenia.

Adult↗

PubMedDate not supplied

Use of TLC and multivariate mathematical statistical methods to study the interaction of monoamine oxidase inhibitory drugs with amino acids.

The interaction of 17 monoamine oxidase inhibitory drugs (propargylamine derivatives) with amino acids was studied by charge-transfer chromatography. The data set was evaluated by principal component analysis (PCA). To assess the effect of the information loss caused by normalization, PCA was separately carried out on the covariance and on the correlation matrix. The strength and selectivity of interaction was separated by the spectral mapping technique. Calculation proved that the amino group of the drugs interacted with the second carboxyl group of dicarboxylic amino acids, and that the interaction was of electrostatic character. This finding made probable the direct interaction between the drugs and the target enzyme or enzymes. The results of both PCA methods were similar. However, coordinates of the spectral map showed only slight correlation with the corresponding coordinates of the two-dimensional nonlinear maps proving the different information content of the methods.

Amino Acids↗

PubMed2002

Analysis of comparative data using generalized estimating equations.

It is widely acknowledged that the analysis of comparative data from related species should be performed taking into account their phylogenetic relationships. We introduce a new method, based on the use of generalized estimating equations (GEE), for the analysis of comparative data. The principle is to incorporate, in the modelling process, a correlation matrix that specifies the dependence among observations. This matrix is obtained from the phylogenetic tree of the studied species. Using this approach, a variety of distributions (discrete or continuous) can be analysed using a generalized linear modelling framework, phylogenies with multichotomies can be analysed, and there is no need to estimate ancestral character state. A simulation study showed that the proposed approach has good statistical properties with a type-I error rate close to the nominal 5%, and statistical power to detect correlated evolution between two characters which increases with the strength of the correlation. The proposed approach performs well for the analysis of discrete characters. We illustrate our approach with some data on macro-ecological correlates in birds. Some extensions of the use of GEE are discussed.

Animals↗

PubMed2003

Correlative coherence analysis: variation from intrinsic and extrinsic sources in competing populations.

The concept of the correlation between two signals is generalized to the correlative coherence of a set of n signals by introducing a Shannon-Weaver-type measure of the entropy of the normalized eigenvalues of the n-dimensional correlation matrix associated with the set of signals. Properties of this measure are stated for canonical cases. The measure is then used to evaluate which subsets of a particular set of n signals are more or less coherent. This set of signals comprises extrinsic, stochastic resource inputs and the population trajectories obtained from simulations of a discrete time model of competing biological populations driven by these resource inputs. The analysis reveals that, at low levels of competition, the correlative coherence of the combined system of intrinsic population and extrinsic resource variables is relatively low, but increases with increasing variation in the resources. Further, at intermediate and high competition levels, the correlative coherence depends more strongly on competition than entrainment of stochasticity in the extrinsic resource variables. Density dependence has the effect of amplifying variation in noise only when this variation is relatively large. Also, chaotic systems appear to be entrained by sufficiently noisy environmental inputs.

Analysis of Variance↗

PubMed1988

Craniofacial characteristics in patients with obstructive sleep apneas syndrome.

Obstructive sleep apneas syndrome (OSAS) has been associated with a clinical reduction of the pharyngeal spaces. To define whether predisposing skeletal craniofacial conditions exist in OSAS patients, 32 OSAS adult patients were compared in a cephalometric investigation with a control sample of 40 adults with ideal dentofacial traits. A t-test assessed the statistical significance of the differences in the two groups; correlation matrix tabulation and discriminant function analysis helped in the identification of the influence of different variables in segregation of the two populations. The following observations were made: There were no differences in maxillary or mandibular prognathism between the two groups. The sagittal dimension of the cranial base was significantly reduced in the OSAS sample, as was the bony pharyngeal opening and maxillary length. This posterior facial compression was associated with increased lower face height (p less than 0.01 in all cases). There were significant correlations in both groups between cranial base length or angulation and pharyngeal opening (p less than 0.01). Eighty percent of the population was correctly sorted out using the discriminant function analysis, with only eight controls and five OSAS patients misclassified. However, this analysis suggested that factors other than the cephalometric may be involved in OSAS.

Adult↗

PubMed1991

Patient characteristics and treatment variables associated with apical root resorption during orthodontic treatment.

Multivariate analysis of patient characteristics and clinical variables was carried out with the maximum single maxillary incisor apical root resorption for each patient as the dependent variable. Root lengths were measured in standardized intraoral radiographs from 485 consecutively treated patients, 11.5 to 25 years of age. The correlation matrix revealed a complex pattern of positive and negative associations between the six pretreatment and seven treatment variables. Variables found to contribute significantly to apical root resorption were overjet, history of trauma to maxillary incisors before initiation of treatment, time of treatment with rectangular arch wires, time of treatment with Class II elastics, lip/tongue dysfunction, and/or history of finger-sucking habits persisting beyond the age of 7 years, and impacted maxillary canines to be corrected orthodontically. Clinical application of an open activator was significantly correlated with overjet but negatively correlated with apical root resorption, with the use of rectangular arch wires and/or Class II elastics, and with total banding time.

Adolescent↗

PubMed1997

Meta-analyses of age-cognition relations in adulthood: estimates of linear and nonlinear age effects and structural models.

A meta-analysis was conducted on 91 studies to derive a correlation matrix for adult age, speed of processing, primary-working memory, episodic memory, reasoning, and spatial ability. Structural equation modeling with a single latent common cognitive factor showed that all cognitive measures shared substantial portions of age-related variance. A mediational model revealed that speed of processing and primary-working memory appear to be important mediators of age-related differences in the other measures. However, not all of the age-related influences were mediated. An examination of quadratic age effects and correlational patterns for subsamples under and over 50 years of age revealed that (a) negative age-cognition relations were significant for the 18- to 50-year-old sample and (b) the age-related decline accelerated significantly over the adult life span for variables assessing speed, reasoning, and episodic memory.

Adult↗

PubMed2006

Assessing the limitations of the Banister model in monitoring training.

The aim of this study was to carry out a statistical analysis of the Banister model to verify how useful it is in monitoring the training programmes of elite swimmers. The accuracy, the ill-conditioning and the stability of this model were thus investigated. The training loads of nine elite swimmers, measured over one season, were related to performances with the Banister model. First, to assess accuracy, the 95% bootstrap confidence interval (95% CI) of parameter estimates and modelled performances were calculated. Second, to study ill-conditioning, the correlation matrix of parameter estimates was computed. Finally, to analyse stability, iterative computation was performed with the same data but minus one performance, chosen at random. Performances were related to training loads for all participants (R(2) = 0.79 +/- 0.13, P < 0.05) and the estimation procedure seemed to be stable. Nevertheless, the range of 95% CI values of the most useful parameters for monitoring training was wide: t(a) = 38 (17, 59), t(f) = 19 (6, 32), t(n) = 19 (7, 35), t(g) = 43 (25, 61). Furthermore, some parameters were highly correlated, making their interpretation worthless. We suggest possible ways to deal with these problems and review alternative methods to model the training-performance relationships.

Adult↗

PubMed1992

Glomerular changes in diabetes mellitus.

Ultrastructural, immunohistochemical and biochemical studies have improved our knowledge on the events occurring during the development of diabetic late complications. Immunohistochemical investigations of diabetic kidneys, using antibodies against various components of the extracellular matrix, showed increased collagen type IV (alpha 1,alpha 2-chain) deposition in the mesangial matrix, and a decrease of heparan sulphate proteoglycan in the mesangial matrix and glomerular basement membrane. Changes in matrix components seem to be the underlying cause of the alterations in renal function, as reflected by albuminuria and proteinuria. The occurrence of collagen type III in late diffuse glomerulosclerosis has been interpreted as an irreversible change in glomerular structure. The extent of alteration of the extracellular matrix correlates to a certain extent with the severity of nephropathy of the individual subject. The studies performed to date support the hypothesis that hyperglycaemia, whatever its origin, is the primary cause of diabetic late complications, although the pathobiochemical mechanisms are not yet fully understood. Increased intra- and extracellular levels of glucose and its derivatives are thought to contribute to diabetic tissue dysfunction. Three pathobiochemical theories are favoured in the current discussion: i) the polyol pathway ii) non-enzymatic glycation of proteins iii) direct influence of hyperglycaemia on the synthesis of matrix components. The evidence for the participation of the polyol pathway in the pathogenesis of diabetic nephropathy comes mainly from animal data using aldose reductase inhibitors, but only limited data are available for humans, so that the significance of this pathomechanism cannot yet be determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2006

Correlation between impairment and motor performance during reaching tasks in subjects with spastic hemiparesis.

OBJECTIVE: The main purposes of this study were to examine, in subjects with chronic hemiparesis following a stroke: (i) the correlations between tests of muscle tone, stiffness, spasticity, paresis and co-contraction, and (ii) the correlations of these tests and measurements of impairment to upper extremity motor performance. DESIGN: Prospective, cross-sectional, correlation matrix using sample of convenience. SUBJECTS: Thirteen subjects with chronic hemiparesis secondary to a cerebrovascular accident (stroke) were tested. METHODS: Subjects were assessed using the Fugl-Meyer Upper Extremity Motor Assessment, modified Ashworth scale, deep tendon reflexes, and muscle characteristics that included quantification of muscle stiffness, paresis and co-contraction during a voluntary reaching task and during passive movements. Surface electromyographic and myotonometric muscle stiffness data were obtained during movement trials. RESULTS: Biceps and triceps brachii muscle paresis and excess biceps brachii co-contraction during voluntary reaching had the highest correlations to decreased motor performance. Muscle tone measurements did not have significant correlations to upper extremity performance. CONCLUSION: Paresis of elbow flexors and extensors and excess co-contraction of the biceps brachii during voluntary reaching appear to be most predictive of upper extremity motor performance. Results are discussed in relation to the specific challenges these findings pose for spastic paresis clinical management.

Aged↗

PubMed2004

Sample size calculations for controlled clinical trials using generalized estimating equations (GEE).

OBJECTIVES: Clinical trials with correlated response data based on generalized estimating equations (GEE) have become increasingly popular as they require smaller samples than classical methods that ignore the clustered nature of the data. We have recently derived the recommendation to use the independence estimating equations (IEE) as primary analysis in most controlled clinical trials instead of GEE with estimated correlations. Although several approaches for sample size and power calculation have been proposed, we have shown that most of these procedures are very specific and not as general as required for designing clinical trials. METHODS: We extended the previously developed SAS macro GEESIZE to overcome this restriction. Specifically, we have added the option of an independence working correlation matrix required for the IEE. Additionally, we have reformulated the hypotheses to allow for coding that includes an intercept term instead of the previously used analysis of variance coding. RESULTS: To demonstrate the validity of GEESIZE we investigate the calculated sample sizes for specific models where closed formulae are available. For illustration, we utilize GEESIZE for planning a new trial on the treatment of hypertension and thereby exemplify its flexibility. CONCLUSIONS: We show that our freely available macro is a very general and useful tool for sample size calculation purposes in clinical trials with correlated data.

Cluster Analysis↗

PubMed1987

Evidence for a role of the major glycoprotein in the structural maintenance of the pig zona pellucida.

The functional domains of the glycoproteins of the pig zona pellucida have been analysed using lectin binding, peptide mapping, and immunoblotting in conjunction with analysis by high-resolution two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and protein detection with the silver-based colour stain. Two of the pig zona pellucida glycoproteins identified in 2D-PAGE were differentially proteolysed within the intact matrix by a variety of enzymes. This proteolysis of specific proteins, however, did not affect the suprastructure of the matrix, or inhibit spermatozoa from adhering to the surface of the zona pellucida. The major glycoprotein appears to be involved in the structural maintenance of the zona pellucida because dissolution of the matrix correlated with proteolysis of this glycoprotein by proteinase K. These glycoproteins were further evaluated by lectin blotting with Ricinus communis agglutinin (RCA) and wheat germ agglutinin (WGA) before and after proteolysis of zona pellucida with trypsin. The lectins bound to all charge species of the three major zona pellucida glycoproteins. Only the most acidic components of the major glycoprotein family, which are not extensively digested, were recognized by these lectins after proteolysis. These studies provide evidence that the major glycoprotein family I of the pig zona pellucida is primarily responsible for maintaining the integrity of the matrix.

Animals↗

PubMed2004

Measurement of spinal mobility in ankylosing spondylitis: comparison of occiput-to-wall and tragus-to-wall distance.

OBJECTIVE: To investigate if the tragus-to-wall distance (TWD) is more reliable compared to the occiput-to-wall distance (OWD) as a measurement for thoracic spine extension in patients with ankylosing spondylitis (AS). METHODS: Data from the OASIS cohort, an international longitudinal observational study on outcome in AS, were used. Measurements of OWD and TWD were performed at baseline and at 6, 12, 18, and 24 months. Paired data of Tx and Tx+6 months were used to perform test-retest measurements (intraclass correlations, limits of agreement, and interperiod correlation matrix). Bland and Altman plots were constructed to investigate the agreement between both observations, assuming that there was no true change between 0 and 6 months. To investigate whether a change in disease activity would have influenced the results, limits of agreement were calculated in a subgroup of patients with a stable Bath Ankylosing Spondylitis Disease Activity Index (BASDAI; defined as a maximum BASDAI change of +/- 1) between T0 and T6 and compared with the results of the whole group. Limits of agreement were also calculated for kyphosed patients only. RESULTS: The test-retest intraclass correlations were between 0.94 and 0.96 for OWD and between 0.93 and 0.95 for TWD. The direct measurement-remeasurement correlation calculated by extrapolation of the interperiod correlation regression line was 0.92 for OWD and 0.90 for TWD. OWD and TWD showed comparable reliability on the entire value of scores. The lower 95% limit of agreement was between -3.4 cm and -2.5 cm for OWD and between -3.4 cm and -3.1 cm for TWD. The upper limit of agreement was between 3.1 cm and 4.2 cm for OWD and between 2.9 cm and 3.9 cm for TWD. In all patients as well as in kyphosed patients only, limits of agreement were comparable between OWD and TWD. The patterns of the scatterplots according to Bland and Altman were similar for OWD and TWD. Measurement error was more pronounced in kyphosed patients compared to patients with a normal thoracic extension. However, over the entire range of kyphosis, measurement error was similar. CONCLUSION: OWD and TWD are equally reliable in assessing thoracic spine extension. Although the TWD is in general easier to perform in AS patients compared to OWD, we recommend the OWD measurement over TWD: in OWD measurement a value of zero easily distinguishes patients with normal thoracic spine extension from kyphosed patients.

Adult↗