SEARCH · PubMed Health

Results for “correlation matrix”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources

PubMed2006

Statistical analysis of test-day milk yields using random regression models for the comparison of feeding groups during the lactation period.

Random regression models are widely used in the field of animal breeding for the genetic evaluation of daily milk yields from different test days. These models are capable of handling different environmental effects on the respective test day, and they describe the characteristics of the course of the lactation period by using suitable covariates with fixed and random regression coefficients. As the numerically expensive estimation of parameters is already part of advanced computer software, modifications of random regression models will considerably grow in importance for statistical evaluations of nutrition and behaviour experiments with animals. Random regression models belong to the large class of linear mixed models. Thus, when choosing a model, or more precisely, when selecting a suitable covariance structure of the random effects, the information criteria of Akaike and Schwarz can be used. In this study, the fitting of random regression models for a statistical analysis of a feeding experiment with dairy cows is illustrated under application of the program package SAS. For each of the feeding groups, lactation curves modelled by covariates with fixed regression coefficients are estimated simultaneously. With the help of the fixed regression coefficients, differences between the groups are estimated and then tested for significance. The covariance structure of the random and subject-specific effects and the serial correlation matrix are selected by using information criteria and by estimating correlations between repeated measurements. For the verification of the selected model and the alternative models, mean values and standard deviations estimated with ordinary least square residuals are used.

Animal Feed↗

PubMed1992

O2 delivery at VO2max and oxidative capacity in muscles of standardbred horses.

The purpose of this study was to describe the relationships between 16 physiological, biochemical, and morphological variables presumed to relate to the oxidative capacity in quadriceps muscles or muscle parts in Standardbred horses. The variables included O2 delivery (blood flow) and mean capillary transit time (MTT) during treadmill locomotion at whole animal maximal O2 consumption (VO2max, 134 +/- 2 ml.min-1 x kg-1), capillary density and capillary-to-fiber ratio, myoglobin concentration, oxidative enzyme activities, glycolytic enzyme activities, fiber type populations, and fiber size. These components of muscle metabolic capacity were found to be interrelated to varying degrees using correlation matrix analysis, with lactate dehydrogenase activity showing the most significant correlations (n = 14) with other variables. Most of the "oxidative" variables occurred in the highest quantities in the deepest muscle of the group (vastus intermedius) and in the deepest parts of the other quadriceps muscles where the highest proportions of type I fibers were localized. The highest blood flow measured with microspheres in the muscle group during exercise was in vastus intermedius muscle (145 ml.min-1 x 100 g-1), and the lowest was in the superficial part of rectus femoris muscle (32 ml.min-1 x 100 g-1). Average muscle blood flow during exercise at whole animal VO2max was 116 ml.min-1 x 100 g-1. Because skeletal muscle comprised 43% of total body mass (453 +/- 34 kg), total muscle blood flow was estimated at 226 l/min, which was approximately 78% of total cardiac output (288 l/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2002

Implant dentistry in predoctoral education: the elective approach.

In response to interest by dental students and patient needs, an elective program in implant dentistry was started at the University of Detroit Mercy School of Dentistry (UDM) in the summer of 1994. The 1-year program is offered to a group of 10 senior students out of a class of 72. Implant treatment is provided to selected edentulous and partially edentulous patients. Predoctoral students participate in diagnosis and treatment planning, assist in surgical placement, and perform the prosthodontic procedures. A survey was sent to 160 UDM graduates, and 90 responded. Out of the 90 respondents, 35% had participated in the elective implant program and 65% had not. A Pearson correlation matrix was used to analyze their responses. A stronger positive correlation with offering and restoring implants was seen in graduates who had completed the elective program in implant dentistry.

Attitude of Health Personnel↗

PubMed2004

Resistin levels in patients with obstructive sleep apnoea syndrome--the link to subclinical inflammation?

BACKGROUND: The role of resistin, a "new" white adipose tissue hormone, still needs to be established. Its linkage to insulin sensitivity and body mass was controversial in previous studies. MATERIAL/METHODS: Twenty obese patients (BMI: 32.1+/-6.9 kg/m2 ) with obstructive sleep apnoea syndrome (OSAS) (Apnoea-Hypopnoea Index: 48.6+/-19.1, underwent measurements of resistin, interleukin-6 (IL-6), intracellular adhesion molecule-1 (ICAM-1), CRP and the insulin sensitivity index (ISI) by hyperinsulinaemic euglycaemic clamp before, 2 days and 2 months after onset of CPAP treatment. RESULTS: Resistin remained unchanged during CPAP-therapy and was negatively correlated to ISI (r=-0.359; p=0.006), the latter was significantly improved by CPAP (p<0.001). In a correlation matrix, IL-6 and ICAM-1 were significantly (p=0.001) correlated to resistin (p=0.614 and 0.427). Changes of inflammatory markers under CPAP treatment were related to AHI, as well as resistin changes. CONCLUSIONS: In agreement with previous investigations, we could only demonstrate a weak linkage between ISI and resistin. However, at least in obese patients with OSAS, there is a close relation to subclinical inflammation (IL-6) and endothelial activation (ICAM-1).

Body Mass Index↗

PubMed1993

All-night dynamics of the human sleep EEG.

The dynamics of the sleep EEG were investigated by all-night spectral analysis of 51 sleep records. Power density was calculated for 1-Hz bins in the 0.25-25.0 Hz range. Values in non-rapid-eye-movement sleep (NREMS) were higher than in REMS in the 0.25-16.0 Hz range, and lower in the 18.25-22.0 Hz range. Power density in the 0.25-12.0 Hz range showed a declining trend over the first four NREMS episodes, which, depending on the frequency bin, could be approximated by non-linear or linear decay functions. In the frequency range of sleep spindles (12.25-15.0 Hz), power density in the 13.25-15.0 Hz band showed an increasing trend between NREMS episode 2 and NREMS episode 4. A correlation matrix of 25 1-Hz bins revealed for NREMS a negative correlation between slow-wave activity (SWA; 0.25-4.0 Hz) and activity in the spindle frequency range. This negative correlation was highest in the first NREMS episode and diminished progressively over the subsequent NREMS episodes. Within NREMS episodes, the values in the spindle frequency range showed a U-shaped time course, the trough coinciding with a high level of SWA. By contrast, in both the early and late part of the episode the two types of activity changed in the same direction. The results are consistent with recent electrophysiological studies indicating that the establishment of NREMS is associated with a progressive hyperpolarization of thalamocortical neurons during which the membrane potential exhibits oscillations first in the spindle frequency range and then in the range of SWA.

Journal Article↗

PubMed1992

Multivariate analyses of CT findings in typical schizophrenia and atypical psychosis.

In order to investigate the brain morphological differences between typical schizophrenia and atypical psychosis, the brain CTs of 41 patients with typical schizophrenia, 27 patients with atypical psychosis (ATP), and 20 controls were examined. The schizophrenics had larger values for 9 CT indices, i.e., interhemispheric fissure (IHF) index, VBR, 2 lateral ventricles (L-V) and 3rd ventricle (III-V) indices, and 4 sylvian fissure (SF) indices, while the values of ATP patients for 3 SF indices were greater than for the controls. Moreover, the schizophrenics had greater III-V and L-V indices than the ATP patients. The correlation matrix of CT indices indicates that the III-V index correlated well with the other CT indices, whereas the VBR, IHF and right SF indices did not. Therefore, it was speculated that there might be 3 subgroups, each of which has a main focus of alteration in the above-mentioned regions. Therefore, all the cases were divided by means of a cluster analysis into 5 groups. Group I, which contained mainly normal controls, and Group II, which consisted mainly of atypical psychosis patients, had no abnormal CT findings. Group III, which comprised mainly ATP patients and paranoid type schizophrenics, had right SF enlargement. Group IV, which showed significant IHF enlargement, and the residue group, which had larger VBR and significant left SF enlargement, consisted mostly of schizophrenics. Thus, our results suggest that the classification by CT data corresponds on the whole to our clinical diagnosis, according to which schizophrenic psychosis is divided into typical schizophrenia and atypical psychosis, and that each of the two psychosis groups may be further classified into distinct subgroups.

Adult↗

PubMed2003

A heuristic for the degrees of freedom of statistics based on multiple variance parameters.

In neuroimaging, data are often modeled using general linear models. Here, we focus on GLMs with error covariances which are modeled as a linear combination of multiple variance/covariance components. Each of these components is weighted by one variance parameter. In many analyses variance parameters are estimated using restricted maximum likelihood (ReML). Most classical approaches assume the error covariance matrix can be factorized into a single variance parameter and a nonspherical correlation matrix. In this context, the F test based on a single variance parameter, with a suitable correction to the degrees of freedom, is the standard inference tool. This correction can also be adapted to models with multiple variance parameters. However, this extension overlooks the uncertainty about the variance parameter estimates and P values tend to be underestimated. Here, we show how one can overcome this problem to render the F test more exact. This issue is important, because serial correlations in fMRI time series are generally modeled using multiple variance parameters. Another application is to hierarchical linear models, which are used for modeling multisubject data. To illustrate our approach, we apply it to some typical modeling scenarios in fMRI data analysis.

Algorithms↗

PubMed1989

Age, sex and suicide rates within birth cohorts in England and Wales.

The relationships between suicide rates at different ages within male and female birth cohorts in England and Wales are examined. There is a sex difference in the pattern of mean correlations of within-cohort rates for various time intervals, with females showing a significant negative correlation between rates separated by 10-15 years. The full correlation matrix of age-specific rates indicates that this negative mean interval correlation is due to negative correlations between rates at age 35-44 years and rates at other ages. This suggests that the acceleration-deceleration model of suicide may be applicable to female rates, with a reduction in suicide associated with pregnancy and motherhood and a rebound increase in rates thereafter.

Adolescent↗

PubMed1989

Multivariate mutation-selection balance with constrained pleiotropic effects.

A multivariate quantitative genetic model is analyzed that is based on the assumption that the genetic variation at a locus j primarily influences an underlying physiological variable yj, while influence on the genotypic values is determined by a kind of "developmental function" which is not changed by mutations at this locus. Assuming additivity among loci the developmental function becomes a linear transformation of the underlying variables y onto the genotypic values x, x = By. In this way the pleiotropic effects become constrained by the structure of the B-matrix. The equilibrium variance under mutation-stabilizing selection balance in infinite and finite populations is derived by using the house of cards approximation. The results are compared to the predictions given by M. Turelli in 1985 for pleiotropic two-character models. It is shown that the B-matrix model gives the same results as Turelli's five-allele model, suggesting that the crucial factor determining the equilibrium variance in multivariate models with pleiotropy is the assumption about constraints on the pleiotropic effects, and not the number of alleles as proposed by Turelli. Finally it is shown that under Gaussian stabilizing selection the structure of the B-matrix has effectively no influence on the mean equilibrium fitness of an infinite population. Hence the B-matrix and consequently to some extent also the structure of the genetic correlation matrix is an almost neutral character. The consequences for the evolution of genetic covariance matrices are discussed.

Genetic Variation↗

PubMed2001

Relationship of numbing to alexithymia, apathy, and depression.

The present study assessed the relationship between numbing and three associated conditions of alexithymia, apathy, and depression, utilizing data collected on 353 Vietnam combat veterans diagnosed with Posttraumatic Stress Disorder from in- and out-patient settings and an outreach center at various Department of Veterans Affairs Medical centers. All subjects completed four self-report measures: the Glover Numbing Scale, the Beck Depression Inventory, the Apathy Evaluation Scale, and the Toronto Alexithymia Scale-20. The correlation matrix indicated that scores on the four measures were moderately to highly correlated. Principal components analysis with a varimax rotation indicated a five-factor solution that provided evidence for the factorial validity of each of the constructs assessed. Results of the factor analysis of items from the four measures were consistent with numbing being a separate and distinct construct from alexithymia, apathy, and depression. In general, results indicated that all constructs measured were separate and distinct from one another.

Affective Symptoms↗

PubMed1994

Genetic structure of the Utah Mormons: comparison of results based on RFLPs, blood groups, migration matrices, isonymy, and pedigrees.

The genetic structure of the Utah Mormon population is examined using 25 blood group and 47 RFLP alleles obtained from 442 subjects living in 8 geographic subdivisions. Nei's GST was 0.013 (p < 0.002) for the RFLP data and 0.012 (p > 0.4) for the blood group data, showing that only 1% of the genetic variance in this population can be attributed to subdivision effects. A comparison of intersubdivision distance matrices based on blood groups, RFLPs, migration matrices, isonymy, and pedigrees shows that genetic distances have relatively low and nonsignificant correlations with the other three types of data. However, the correlations based on RFLPs are considerably higher than those based on blood groups. Relationship matrices based on interindividual allele sharing were compared with known genealogical kinship coefficients between each pair of individuals. The correlation between the blood group and RFLP relationship matrices was small but marginally significant using the Mantel test (r = 0.014, p < 0.06). The RFLP relationship matrix correlated more highly with genealogical kinship than did the blood group relationship matrix (r = 0.023, p < 0.0001 and r = 0.012, p < 0.001, respectively). These correlations increased by approximately one order of magnitude when pairs of subjects having zero kinship coefficients were excluded. These results show that genetic distances derived from RFLPs correlate more strongly with other types of kinship than do distances based on blood groups. This probably reflects the fact that RFLPs are more neutral, have frequencies that are more accurately estimated, and contain more information about DNA sequence variation.

Blood Group Antigens↗

PubMed2007

Interspecific analysis of covariance structure in the masticatory apparatus of galagos.

The primate masticatory apparatus (MA) is a functionally integrated set of features, each of which performs important functions in biting, ingestive, and chewing behaviors. A comparison of morphological covariance structure among species for these MA features will help us to further understand the evolutionary history of this region. In this exploratory analysis, the covariance structure of the MA is compared across seven galago species to investigate 1) whether there are differences in covariance structure in this region, and 2) if so, how has this covariation changed with respect to size, MA form, diet, and/or phylogeny? Ten measurements of the MA functionally related to bite force production and load resistance were obtained from 218 adults of seven galago species. Correlation matrices were generated for these 10 dimensions and compared among species via matrix correlations and Mantel tests. Subsequently, pairwise covariance disparity in the MA was estimated as a measure of difference in covariance structure between species. Covariance disparity estimates were correlated with pairwise distances related to differences in body size, MA size and shape, genetic distance (based on cytochrome-b sequences) and percentage of dietary foods to determine whether one or more of these factors is linked to differences in covariance structure. Galagos differ in MA covariance structure. Body size appears to be a major factor correlated with differences in covariance structure among galagos. The largest galago species, Otolemur crassicaudatus, exhibits large differences in body mass and covariance structure relative to other galagos, and thus plays a primary role in creating this association. MA size and shape do not correlate with covariance structure when body mass is held constant. Diet also shows no association. Genetic distance is significantly negatively correlated with covariance disparity when body mass is held constant, but this correlation appears to be a function of the small body size and large genetic distance for Galagoides demidoff. These exploratory results indicate that changing body size may have been a key factor in the evolution of the galago MA.

Animals↗

PubMed1992

Differences between children of depressed and non-depressed mothers: locus of control, anxiety and self-esteem: a research note.

Fifty-six mothers (26 depressed and 30 non-depressed) and their children were assessed on three measures: locus of control, anxiety and self-esteem. T-tests of results indicated significant differences between the groups of mothers across all three measures. There were significant differences between the two groups of children on state anxiety, total score on the self-esteem measure and social self-esteem, with the children of non-depressed mothers being lower on state anxiety and showing higher levels of self-esteem. Other aspects of self-esteem and locus of control did not show significant differences between the groups. A correlation matrix revealed that trait anxiety in the children of depressed mothers was significantly correlated with the mothers' depression, but not the mothers' anxiety. An analysis of discriminant functions found that a more anxious mood state and feelings of fear and worry were associated with the children of the depressed mothers.

Adult↗

PubMed1985

Defining duodenitis: quantitative histological study of mucosal responses and their correlations.

Biopsies from 56 patients with endoscopically normal duodenal bulbs, duodenitis, or duodenal ulceration were studied for counts of plasma cells, polymorphs, and eosinophils and extent of gastric metaplasia, villous atrophy, and mucosal oedema. A correlation matrix showed that the counts of different types of plasma cells were closely correlated with each other and that there was also a close correlation between the presence of intraepithelial polymorphs, villous atrophy, and gastric metaplasia. Cluster and discriminant analysis indicated that the histological changes could be grouped by their statistical association into three simple categories: normal, which includes many cases incorrectly labelled in some classification systems as mild or chronic duodenitis; histologically defined mild duodenitis, characterised by an appreciable plasma cell response and oedema usually with intraepithelial polymorph infiltration and gastric metaplasia; and severe duodenitis, with an appreciable polymorph response and villous atrophy but decreased plasma cells. Decreased plasma cells may be an important indication of peptic ulceration.

Aged↗

PubMed1999

Immunohistochemical distribution of extracellular matrix components and keratin in experimentally induced otitis media.

The distribution of collagen types I, III, and IV and of laminin, fibronectin, and keratin was studied in otitis media experimentally induced by Streptococcus pneumoniae in the chinchilla. The expression of interstitial collagen types I and III and of fibronectin was increased in the subepithelial space that was thickened by inflammation in the acute period of infection. The expression of collagen type IV in the subepithelial space could be seen in the early period. The epithelial cells in the middle ear changed from flat cuboidal to pseudostratified columnar in pneumococcus-inoculated ears, and the number of keratin-positive epithelial cells in the middle ear increased remarkably after infection. These results indicate that changes in epithelial cell differentiation effected by the extracellular matrix correlate with changes in expression of keratin. It is proposed that the extracellular matrix may contribute to tissue repair in the middle ear after bacterial infection by interfering with cell proliferation of epithelial cells and fibroblasts.

Animals↗

PubMed1996

[Fast and accurate numerical method for principal components analysis dealing with large image data sets].

The principal components analysis has been applied to various imaging studies in nuclear medicine. This technical report describes a fast and accurate numerical method of calculating eigenvalues and eigenvectors in the principal components analysis dealing with larger image data sets. The method employs both data transformation and matrix transpose of original data sets to calculate a variance-covariance or correlation matrix. The method was tested on actual image data sets using a common workstation, confirming faster execution time and efficient accuracy in comparison to a standard method.

Image Processing, Computer-Assisted↗

PubMed2001

A comparison of phenotypic variation and covariation patterns and the role of phylogeny, ecology, and ontogeny during cranial evolution of new world monkeys.

Similarity of genetic and phenotypic variation patterns among populations is important for making quantitative inferences about past evolutionary forces acting to differentiate populations and for evaluating the evolution of relationships among traits in response to new functional and developmental relationships. Here, phenotypic co variance and correlation structure is compared among Platyrrhine Neotropical primates. Comparisons range from among species within a genus to the superfamily level. Matrix correlation followed by Mantel's test and vector correlation among responses to random natural selection vectors (random skewers) were used to compare correlation and variance/covariance matrices of 39 skull traits. Sampling errors involved in matrix estimates were taken into account in comparisons using matrix repeatability to set upper limits for each pairwise comparison. Results indicate that covariance structure is not strictly constant but that the amount of variance pattern divergence observed among taxa is generally low and not associated with taxonomic distance. Specific instances of divergence are identified. There is no correlation between the amount of divergence in covariance patterns among the 16 genera and their phylogenetic distance derived from a conjoint analysis of four already published nuclear gene datasets. In contrast, there is a significant correlation between phylogenetic distance and morphological distance (Mahalanobis distance among genus centroids). This result indicates that while the phenotypic means were evolving during the last 30 millions years of New World monkey evolution, phenotypic covariance structures of Neotropical primate skulls have remained relatively consistent. Neotropical primates can be divided into four major groups based on their feeding habits (fruit-leaves, seed-fruits, insect-fruits, and gum-insect-fruits). Differences in phenotypic covariance structure are correlated with differences in feeding habits, indicating that to some extent changes in interrelationships among skull traits are associated with changes in feeding habits. Finally, common patterns and levels of morphological integration are found among Platyrrhine primates, suggesting that functional/developmental integration could be one major factor keeping covariance structure relatively stable during evolutionary diversification of South American monkeys.

Animals↗

PubMed2004

Chronic treatment with atypical neuroleptics induces striosomal FosB/DeltaFosB expression in rats.

BACKGROUND: Studies have shown that neuroleptics regulate expression of the transcription factor FosB/DeltaFosB in the striatum, including the accumbens and caudate-putamen; however, the striatum is also divided into another structural dimension, the striosome and matrix compartments. The precise distribution of FosB/DeltaFosB induced by chronic neuroleptics in these striatal compartments is poorly understood. METHODS: Rats received either single acute injections or chronic injections of clozapine (0 or 20 mg/kg, intraperitoneally [IP]), olanzapine (0 or 5 mg/kg, IP), or haloperidol (0 or 1.5 mg/kg, IP) for 25 days. The levels and compartmental distribution of FosB/DeltaFosB were examined. RESULTS: Chronic clozapine induced clustered FosB/DeltaFosB expression within striosomes of the caudate-putamen. This pattern was due to increased levels of FosB/DeltaFosB in striosomes within the ventrolateral caudate-putamen and reduced levels of basal FosB/DeltaFosB in the matrix in the entire caudate-putamen. In contrast, chronic haloperidol increased FosB/DeltaFosB equally within the matrix and striosomes throughout the entire caudate-putamen. Chronic olanzapine induced an intermediate pattern. CONCLUSIONS: The relative absence of FosB/DeltaFosB expression in the matrix correlates with the lack of parkinsonism of atypical neuroleptics. Expression of FosB/DeltaFosB in the matrix may contribute to parkinsonism of typical neuroleptics.

Animals↗