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Results for “correlation matrix”

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PubMed1990

Cardiovascular stability during the haemodialysis session: relationship between modelling and impedance parameters.

The percentage of body water, if calculated from impedance, was found to be significantly different from the classic 58%. This supports the view that the evaluation of the dialytic efficiency should be, in the near future, carried out on the basis of a 'two-pool' model instead of the old 'one-pool'. The serial collection of data during a dialytic session supported the hypothesis that, 90 min after the start or, in general, after a body-water loss of about 5%-6%, some fundamental changes in measured indexes (phase angle, systolic pressure, body volumes, correlation matrix) usually appear. Large-scale research, based on an RS 232 interface connected to a computerised program, will probably help in clarifying whether some major intra-dialytic phenomena could in the near future be easily and automatically predicted.

Body Water↗

PubMed2001

Development and validation of a self-efficacy scale for use in British patients with rheumatoid arthritis (RASE).

OBJECTIVE: Current arthritis self-efficacy scales have attracted some criticism. Therefore, the aim of this study was to develop and validate a measure of self-efficacy for use in British rheumatoid arthritis patients [Rheumatoid Arthritis Self-efficacy (RASE) scale]. METHODS: Phase I: item generation of self-management strategies by rheumatology professionals and patients to create a pilot RASE. Phase II: examination of the internal structure (n=88) using correlation coefficients and principal component analysis (PCA) to create the final RASE. Phase III: reliability in 23 patients. Phase IV: comprehension, construct validity and sensitivity to change in 48 rheumatoid arthritis patients undergoing a self-management programme, using correlation coefficients, PCA and inter-item correlation. RESULTS: Phase I: of 166 self-management items generated, 100 commonly cited items were selected for the pilot RASE. Phase II: using a correlation matrix and PCA, a 28-item RASE was created. Phase III: good 4-week reliability was seen (r=0.889, P<0.001). Phase IV: the final RASE was shown to be independent of mood, disease status and disability and weakly associated with other self-efficacy scales (r=0.313, P<0.05). The RASE was sensitive to change following an education programme (+5.167, P<0.025), and was associated with behaviour initiation (r=0.35, P<0.01). CONCLUSIONS: Careful construction means that the RASE examines beliefs in potential ability to perform tasks, rather than actual ability, performance or outcome expectancy. It shows good face validity and reliability, plus reasonable construct validity and sensitivity. Further studies are needed to support the validation of this new scale.

Adult↗

PubMed2000

Topography of clonidine-induced electroencephalographic changes evaluated by principal component analysis.

BACKGROUND: Principal component analysis is a multivariate statistical technique to facilitate the evaluation of complex data dimensions. In this study, principle component analysis was used to reduce the large number of variables from multichannel electroencephalographic recordings to a few components describing changes of spatial brain electric activity after intravenous clonidine. METHODS: Seven healthy volunteers (age, 26 +/- 3 [SD] yr) were included in a double-blind crossover study with intravenous clonidine (1.5 and 3.0 microg/kg). A spontaneous electroencephalogram was recorded by 26 leads and quantified by standard fast Fourier transformation in the delta, theta, alpha, and beta bands. Principle component analysis derived from a correlation matrix calculated between all electroencephalographic leads (26 x 26 leads) separately within each classic frequency band. The basic application level of principle component analysis resulted in components representing clusters of electrodes positions that were differently affected by clonidine. Subjective criteria of drowsiness and anxiety were rated by visual analog scales. RESULTS: Topography of clonidine-induced electroencephalographic changes could be attributed to two independent spatial components in each classic frequency band, explaining at least 85% of total variance. The most prominent effects of clonidine were increases in the delta band over centroparietooiccipital areas and decreases in the alpha band over parietooccipital regions. Clonidine administration resulted in subjective drowsiness. CONCLUSIONS: Data from the current study supported the fact that spatial principle component analysis is a useful multivariate statistical procedure to evaluate significant signal changes from multichannel electroencephalographic recordings and to describe the topography of the effects. The clonidine-related changes seen here were most probably results of its sedative effects.

Adult↗

PubMed2001

Anhedonia in depression and schizophrenia: a reexamination.

The purpose of this study was to utilize factor analysis to help determine whether anhedonia is a symptom of both depression and schizophrenia. Measures of depression, positive and negative symptoms of schizophrenia, and anhedonia were administered to a group of schizophrenic patients (N = 54) and to a group of patients with major depressive disorder (N = 27). The correlation matrix among the various scales was subjected to an oblique exploratory factor analysis. Three factors were extracted, accounting for three quarters of the variance. The first measured depression, the second measured positive symptoms, and the third measured negative symptoms. Anhedonia loaded significantly on the first factor but not on the third, suggesting that it is a symptom of depression rather than schizophrenia. These results were corroborated by means of confirmatory factor analysis. We conclude that anhedonia is a symptom of depression and that it only appears to be a symptom of schizophrenia because it is a component of emotional blunting which is indeed a negative symptom of schizophrenia.

Adult↗

PubMed1981

On the perceived meaning of symptoms.

The importance of understanding the manner in which symptoms are interpreted is generally recognized, but has received relatively little direct research attention. In an attempt to obtain some evidence on the meaning attached to each of a set of 45 symptoms, subjects were asked to rate the symptoms on eight semantic properties. The symptom ratings on the various properties were then correlated and the correlation matrix subjected to a principal components factor analysis. Three factors of perceived meaning emerged. The first factor is defined by the extent to which symptoms are perceived as threatening, disruptive and painful. The second factor consists of the familiarity of symptoms and the perceived personal responsibility for their occurrence. The third factor reflects how embarrassing the symptoms are. This structure of perceived meaning of symptoms is discussed with reference to the literature on delay in seeking medical care.

Decision Making↗

PubMed1989

Development and validation of an instrument to measure patient satisfaction with pharmacy services.

A research program was undertaken to develop and validate a multidimensional measure of patient satisfaction with pharmacy services. A self-administered questionnaire consisting of 44 Likert-type attitudinal items was adapted from the Patient Satisfaction Questionnaire developed by Ware et al. In an iterative scale development process, the adapted questionnaire and its revisions were evaluated in three successive studies conducted on convenience samples (n = 30, 313, 489) of individuals in attendance at family practice clinics in a southwestern city. Methods used to construct multi-item scales measuring separate dimensions of service included principal components factor analysis and item analyses. Acquiescent response set (ARS), the tendency to agree with statements of opinion regardless of content, was measured by the method of matched pairs of items. A partial correlation matrix which controlled for ARS was used as the data in a principal components factor analysis in an effort to reduce the biasing effect of ARS on factor analytic outcomes. Dimensions of satisfaction identified were Explanation, Consideration, Technical Competence, Financial Aspects, Accessibility, Drug Efficacy, OTC (over-the-counter) Product Availability, and Quality of the Drug Product. Questionnaire revision is suggested to confirm the validity of the latter two dimensions Future research should examine the relationship between separate dimensions of satisfaction and other patient attitudes and behaviors, and the convergence between this instrument and other measures of patient satisfaction with pharmacy services.

Adolescent↗

PubMed1985

The relationship between anthropometric, postural, muscular, and mobility characteristics of males ages 18-55.

Three hundred twenty-one males, ages 18-55, had standardized tests to determine height, weight, Davenport Index, leg length inequality, determination of flexion and extension torques, flexion/extension balance, range of motion, straight leg raising, and lumbar lordosis. A total of 106 (33.0%) had never experienced low-back symptoms; 144 (44.9%) had or were having moderate low-back pain (LBP); and 71 (22.1%) had or were having severe low-back symptoms. These three subgroups showed no significant differences in height, weight, Davenport Index, lumbar lordosis, or leg length inequalities. LBP patients had less flexor and extensor strength and were flexor overpowered, had diminished range of motion for spinal extension and axial rotation (P = 0.003, P = 0.0005), and diminished straight leg raising capacity (P = 0.04). A multivariate correlation matrix demonstrated no typical pattern of associated abnormalities except a diminished spinal range of motion in one plane was associated with the anticipated diminishment in all other planes of motion, and often with greater restrictions of straight leg raising tests.

Adolescent↗

PubMed1991

Comparison of computerized and examiner-administered neurobehavioral testing techniques.

To better understand the relationship of newly developed computerized neurobehavioral tests to their examiner-administered counterparts, performance on four pairs of tests was compared among 185 solvent-exposed workers in the paint manufacturing industry. Two approaches to the comparison of the test methods (computer or examiner) were employed: (1) the multitrait-multimethod correlation matrix and (2) linear regression modeling of the difference scores between pairs of tests (same functional domain, different test formats). The data revealed that the validity criteria of the multitrait-multimethod technique were met for the tests of simple visual reaction time and attention-concentration (digit symbol substitution). Linear regression analyses demonstrated that the digit symbol substitution and visual memory test pairs were differentially affected by age, vocabulary, solvent exposure, or manual dexterity. Overall, this latter approach holds promise as a means of understanding test format similarities and differences.

Adult↗

PubMed2005

Fine particulate air pollution and cardiorespiratory effects in the elderly.

BACKGROUND: Past studies of air pollution effects among sensitive subgroups have produced inconsistent results. Our objective was to determine relationships between various measures of air pollution and cardiorespiratory effects in older subjects. METHODS: We conducted a study that included repeated measurements of pulmonary function (arterial oxygen saturation) and cardiac function (heart rate and blood pressure) in a panel of 88 subjects (>57 years of age) in Seattle during the years 1999 to 2001. Subjects were healthy or had lung or heart disease. Each subject participated in sessions of 10 consecutive days of exposure monitoring and collection of health outcomes for up to 2 sessions. Associations between health outcomes and indoor, outdoor, and personal measures of particulate matter </=2.5 micrometers (PM2.5) or particulate matter </=10 micrometers (PM10) were evaluated using generalized estimating equations with an exchangeable working correlation matrix and robust standard errors. The model included terms for the within-subject, within-session effect; the within- subject, between-session effect; and an interaction term for medication usage. The model controlled for temperature, relative humidity, body mass index, and age. RESULTS: Associations between air pollution and health measurements were found primarily in healthy subjects. Healthy subjects taking no medications had decreases in heart rate associated with indoor and outdoor PM2.5 and PM10. Healthy subjects on medication had small increases in systolic blood pressure associated with indoor PM2.5 and outdoor PM10. Heterogeneity analysis found differences among the health groups for associations with particulate air pollution in heart rate but not in blood pressure. CONCLUSION: Modest concentrations of air pollutants were associated with small changes in cardiac function.

Aged↗

PubMed2003

Construct validity of the prenatal attachment inventory: a confirmatory factor analysis approach.

The purpose of this study was to test the construct validity of the Prenatal Attachment Inventory (PAI) by using Confirmatory Factor Analysis (CFA). The PAI was developed by Muller (1989, 1993), and consists of 21 Likert-type items arranged on a 4-point response set ranging from " almost always " to " almost never. " A sample of 349 pregnant women in their third trimester was recruited from obstetrical outpatient and inpatient centers, including high-risk and low-risk pregnancy units, and childbirth education classes. Confirmatory factor analysis of the instrument yielded the result that all items have a significant factor loading. There were no negative error variances, no factor correlations greater than one, and no extremely large error variance. The indicator reliabilities ranged from.2 to.5. Moreover, the correlation matrix indicated that all PAI items were significantly related to one another at p <.01. These 21 items explained 79 % of variance in maternal fetal attachment (MFA). The overall measurement model fit indices showed that the hypothesized model fit the data well after two modifications ( 2/df = 2.12, standardized root mean square residual =.05, goodness-of-fit index =.90, critical N = 204.5). The findings indicate that Muller's PAI is a valid instrument for research with pregnant women. Researchers can use this instrument for future research studies in the health care of pregnant women. Nursing educators and clinicians can use this instrument to assess expectant mothers' level of MFA.

Adolescent↗

PubMed2006

Evidence for a Müllerian mimetic radiation in Asian pitvipers.

Müllerian mimicry, in which toxic species gain mutual protection from shared warning signals, is poorly understood in vertebrates, reflecting a paucity of examples. Indirect evidence for mimicry is found if monophyletic species or clades show parallel geographic variation in warning patterns. Here, we evaluate a hypothesis of Müllerian mimicry for the pitvipers in Southeast Asia using a phylogeny derived from DNA sequences from four combined mitochondrial regions. Mantel matrix correlation tests show that conspicuous red colour pattern elements are significantly associated with sympatric and parapatric populations in four genera. To our knowledge, this represents the first evidence of a Müllerian mimetic radiation in vipers. The putative mimetic patterns are rarely found in females. This appears paradoxical in light of the Müllerian prediction of monomorphism, but may be explained by divergent selection pressures on the sexes, which have different behaviours. We suggest that biased predation on active males causes selection for protective warning coloration, whereas crypsis is favoured in relatively sedentary females.

Animals↗

PubMed2004

Stochastic dynamical model for stock-stock correlations.

We propose a model of coupled random walks for stock-stock correlations. The walks in the model are coupled via a mechanism that the displacement (price change) of each walk (stock) is activated by the price gradients over some underlying network. We assume that the network has two underlying structures, describing the correlations among the stocks of the whole market and among those within individual groups, respectively, each with a coupling parameter controlling the degree of correlation. The model provides the interpretation of the features displayed in the distribution of the eigenvalues for the correlation matrix of real market on the level of time sequences. We verify that such modeling indeed gives good fitting for the market data of US stocks.

Journal Article↗

PubMed2004

Voronoi and void statistics for superhomogeneous point processes.

We study the Voronoi and void statistics of superhomogeneous (or hyperuniform) point patterns in which the infinite-wavelength density fluctuations vanish. Superhomogeneous or hyperuniform point patterns arise in one-component plasmas, primordial density fluctuations in the Universe, and jammed hard-particle packings. We specifically analyze a certain one-dimensional model by studying size fluctuations and correlations of the associated Voronoi cells. We derive exact results for the complete joint statistics of the size of two Voronoi cells. We also provide a sum rule that the correlation matrix for the Voronoi cells must obey in any space dimension. In contrast to the conventional picture of superhomogeneous systems, we show that infinitely large Voronoi cells or voids can exist in superhomogeneous point processes in any dimension. We also present two heuristic conditions to identify and classify any superhomogeneous point process in terms of the asymptotic behavior of the void size distribution.

Journal Article↗

PubMed2004

Semantic graphs and associative memories.

Graphs have been increasingly utilized in the characterization of complex networks from diverse origins, including different kinds of semantic networks. Human memories are associative and are known to support complex semantic nets; these nets are represented by graphs. However, it is not known how the brain can sustain these semantic graphs. The vision of cognitive brain activities, shown by modern functional imaging techniques, assigns renewed value to classical distributed associative memory models. Here we show that these neural network models, also known as correlation matrix memories, naturally support a graph representation of the stored semantic structure. We demonstrate that the adjacency matrix of this graph of associations is just the memory coded with the standard basis of the concept vector space, and that the spectrum of the graph is a code invariant of the memory. As long as the assumptions of the model remain valid this result provides a practical method to predict and modify the evolution of the cognitive dynamics. Also, it could provide us with a way to comprehend how individual brains that map the external reality, almost surely with different particular vector representations, are nevertheless able to communicate and share a common knowledge of the world. We finish presenting adaptive association graphs, an extension of the model that makes use of the tensor product, which provides a solution to the known problem of branching in semantic nets.

Journal Article↗

PubMed2005

Efficient training of multilayer perceptrons using principal component analysis.

A training algorithm for multilayer perceptrons is discussed and studied in detail, which relates to the technique of principal component analysis. The latter is performed with respect to a correlation matrix computed from the example inputs and their target outputs. Typical properties of the training procedure are investigated by means of a statistical physics analysis in models of learning regression and classification tasks. We demonstrate that the procedure requires by far fewer examples for good generalization than traditional online training. For networks with a large number of hidden units we derive the training prescription which achieves, within our model, the optimal generalization behavior.

Journal Article↗

PubMed2006

Spatial recurrence plots.

We propose an extension of the recurrence plot concept to perform quantitative analyzes of roughness and disorder of spatial patterns at a fixed time. We introduce spatial recurrence plots (SRPs) as a graphical representation of the pointwise correlation matrix, in terms of a two-dimensional spatial return plot. This technique is applied to the study of complex patterns generated by coupled map lattices, which are characterized by measures of complexity based on SRPs. We show that the complexity measures we propose for SRPs provide a systematic way of investigating the distribution of spatially coherent structures, such as synchronization domains, in lattice profiles. This approach has potential for many more applications, e.g., in surface roughness analyzes.

Journal Article↗

PubMed2000

Sensitivity of nucleus-nucleus cross sections and atomic-electron effects in dissipative heavy-Ion collisions

We argue that spontaneous microchannel S-matrix correlations and slow spin decoherence result in a sensitivity of the cross sections for strongly dissipative heavy-ion collisions to an arbitrarily small perturbation. Such a sensitivity implies that atomic electrons should influence energetic ( approximately 100 MeV) heavy-ion reactions. The atomic-electron effects are predicted to be approximately 100% of the magnitude of the non-self-averaged oscillating component of the nucleus-nucleus cross sections.

Journal Article↗

PubMed2001

Efficiently learning multilayer perceptrons.

A learning algorithm for multilayer perceptrons is presented which is based on finding the principal components of a correlation matrix computed from the example inputs and their target outputs. For large networks our procedure needs far fewer examples to achieve good generalization than traditional on-line algorithms.

Algorithms↗