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PubMed2006

Assessing seizure dynamics by analysing the correlation structure of multichannel intracranial EEG.

Epileptic seizures are commonly characterized as 'hypersynchronous states'. This habit is doubly misleading, because seizures are not necessarily synchronous and are not unchanging 'states' but dynamic processes. Here the temporal evolution of the correlation structure in the course of 100 focal onset seizures of 60 patients recorded by intracranial multichannel EEG was assessed. To this end a multivariate method was applied that at its core consists of computing the eigenvalue spectrum of the zero-lag correlation matrix of a short sliding window. Our results show that there are clearly observable and statistically significant changes of the correlation structure of focal onset seizures. Specifically, these changes indicate that the zero-lag correlation of multi-channel EEG either remains approximately unchanged or-especially in the case of secondary generalization-decreases during the first half of the seizures. Then correlation gradually increases again before the seizures terminate. This development was qualitatively independent of the anatomical location of the seizure onset zone and therefore seems to be a generic property of focal onset seizures. We suggest that the decorrelation of EEG activity is due to the different propagation times of locally synchronous ictal discharges from the seizure onset zone to other brain areas. Furthermore we speculate that the increase of correlation during the second half of the seizures may be causally related to seizure termination.

Brain↗

PubMed1992

Latent factors in body build of newborns.

The paper is focused on relationships between traits of newborns and on discerning factors characterizing newborns more generally than individual traits. For this purpose a factor analysis was made using 35 somatic traits of 1013 newborns examined in hospitals of Zambrów and Białystok. Main components were found from the correlation matrix, and after the orthogonal rotation of the Varimax type, eight independent factors were identified. The body weight was highly correlated with circumferences of chest, calf, forearm, head, and arm. Body length was correlated with the length of lower extremities, the length of upper extremities was correlated with the length of arm and with the breadth and depth of chest, circumferences of different body parts were correlated with each other, and this was also the case of the thickness of three skin-fat-folds. The following factors were found as a result of the factor analysis (in parentheses there are traits showing highest correlations with a given factor, thus, most suitable for monitoring studies): F1-body weight (thigh circumference), F2-upper extremity length, F3-subcutaneous fat tissue (skin-fat-fold thickness on rib 10), F4-face length and nose diameters (upper-face height), F5-scapular-arm-hip diameters (scapular breadth), F6-trunk length (trunk length), F7-body length (length of lower extremities), and F8-head breadth diameters (mandible breadth).

Adipose Tissue↗

PubMed1995

A correlation significance learning scheme for auto-associative memories.

A new concept called correlation significance for expanding the attraction regions around all the stored vectors (attractors) of an asynchronous auto-associative memory is introduced. Since the well known outer product rule adopts equally-weighted correlation matrix for the neuron connections, the attraction region around each attractor is not maximized. In order to maximize these attraction regions, we devise a rule that all the correlations between two different components of two different stored patterns should be unequally weighted. By this formalism, the connection matrix T of the asynchronous neural network is designed by using the gradient descent approach. Additionally, an exponential type error function is constructed such that the number of successfully stored vectors can be directly examined during the entire learning process. Finally, computer simulations demonstrate the efficiency and capability of this scheme.

Computer Simulation↗

PubMed1987

The specificity of quality-of-life measures among the seriously ill.

The need to address the impacts of serious disease and the effectiveness of interventions has led to the development of numerous measures of the quality of life. The research reported here explores the possibility that widely used measures do not truly distinguish among separate dimensions of the quality of life in a seriously ill population, but reflect a generalized tendency among such individuals to respond negatively to interviewers' questions about their well-being. This research examines three widely used measures--the Sickness Impact Profile (SIP), the Profile of Mood States (POMS), and the McGill Pain Questionnaire (MPQ)--as applied to 536 individuals with recent cancer diagnoses. In a multitrait-multimethod matrix, correlation coefficients among measures believed to reflect the same phenomena are consistently higher than correlation coefficients among measures supposed to reflect different phenomena. In a factor analysis performed on all 536 subjects, the unrotated factor matrix indicates that no single factor explains a preponderance of the variance in individual measures. Orthogonal rotation indicates that subscales from the SIP, POMS, and MPQ generally load on factors defined by the scales of which they are part. These findings were replicated on subsamples of subjects with particularly severe disease. The study suggests that the SIP, POMS, and MPQ measure the specific dimensions their names imply, even among individuals with illnesses posing immediate threats to survival.

Affect↗

PubMed1992

Development of an instrument to assess learning strategies.

Items to measure learning strategies were extracted from students' written narratives about their study and learning habits. A resulting 79-item instrument was administered to 321 graduate and undergraduate students. From factor analysis of the correlation matrix four factors were identified: (I) reflective metacognition, (II) procedural metacognition, (III) rote memorization, and (IV) procrastination. There were significant positive correlations between GPA and Factors I and II and a significant negative correlation between Factor IV and GPA.

Achievement↗

PubMed2004

A multivariate approach to modeling shapes of individual lactation curves in cattle.

Milk test-day records of 5728 lactations of Italian Simmental cows were analyzed with multivariate factor analysis in order to extract 2 common factors, whose scores were used as quantitative measures of 2 main features of lactation curve shape-i.e., the increasing rate of yield in the first part of lactation and the rate of decline of milk yield after the lactation peak. The 2 indices, objectively derived from the correlation matrix of original test-day records, showed a high discriminant power in separating lactation curves with different shapes. The weak correlation between the 2 factors (0.11), together with the high correlation of factors and the total 305-d yield (about 0.70), suggests that an increase in lactation yield could be achieved by acting only on one of the 2 factors related to lactation-curve shape, with the other kept constant at a medium or low value. The suitability of the 2 factors as descriptors of lactation patterns has been confirmed by the relationships found between factor scores and the main environmental effects known to affect the shape of the lactation curve, such as parity and season of calving.

Analysis of Variance↗

PubMed2003

No clear-cut evidence for cadmium-induced renal tubular dysfunction among over 10,000 women in the Japanese general population: a nationwide large-scale survey.

OBJECTIVE: To examine whether environmental exposure to cadmium has been inducing kidney dysfunction among middle-aged women in the general population in Japan. METHODS: This study was conducted in 2000 and 2001. Morning spot urine samples were collected from 10,753 women (mostly aged 35 to 60 years) in ten prefectures all over Japan (thus about 1,000 women per site). Urine samples were analyzed for cadmium (Cd-U), calcium (Ca-U), magnesium (Mg-U), zinc (Zn-U), alpha(1)- and beta(2)-microglobulins (alpha(1)- and beta(2)-MG-U). The urinary analyte concentrations were corrected for creatinine (cr) concentration (i.e., Ucr). The data thus obtained were subjected to statistical evaluation by chi-square test, ANOVA, multiple comparison test, and simple regression analysis (SRA) as well as multiple regression analysis (MRA) including logistic regression analysis (LRA). Log-normal distribution was assumed for Cd-Ucr, alpha(1)-MG-Ucr and beta(2)-MG-Ucr, whereas normal distribution was considered for age, Ca-Ucr, Mg-Ucr and Zn-Ucr. RESULTS: Geometric mean values (GM) of Cd-Ucr were distributed unevenly, depending on the sampling areas, with a grand GM of 1.3 microg/g cr, the highest (3.2 microg/g cr) and lowest GM values(0.8 microg/g cr) being significantly different from GMs of other areas. Correlation matrix analysis with subjects of all ages showed that log alpha(1)-MG-Ucr and log beta(2)-MG-Ucr correlated significantly (r=0.272 and 0.202, respectively) with log Cd-Ucr, but they correlated also with age (r=0.280 and 0.213, respectively). The same analysis with the two selected age groups (41-50 and 51-60 years), however, failed to show close correlation of alpha(1)-MG-Ucr and log beta(2)-MG-Ucr with Cd-Ucr. Both MRA and LRA indicated that age was a confounding factor in the evaluation of the effect of Cd-U on the two MG levels. Whereas the LRA with the all-age group showed a positive influence of log Cd-Ucr on log alpha(1)-MG-Ucr and log beta(2)-MG-Ucr, such effect disappeared in parallel with the disappearance of age effects when LRA was conducted with the two selected age groups. An exceptional observation was the influence of log Cd-Ucr on log alpha(1)-MG-Ucr (but not on log beta(2)-MG-Ucr) in LRA when a cut-off value of 5.00 mg for alpha(1)-MG-U/g cr was applied. Comparison between the low and high Cd-U groups showed that both alpha(1)-MG-Ucr and beta(2)-MG-Ucr were higher in the high Cd-U groups, but prevalence of cases with alpha(1)-MG-Ucr and beta(2)-MG-Ucr in excess of the cut-off values did not differ between the two groups except when a cut-off value of 5.00 mg/g cr was employed for alpha(1)-MG-U. CONCLUSIONS: In over-all evaluation, no clear-cut evidence was obtained in the present study to show that environmental exposure to Cd has induced tubule dysfunction among middle-aged women in the general population in Japan. It might be the case, however, that an increase in alpha(1)-MG-U was associated with Cd exposure. In this sense, it is apparently desirable from public health viewpoints to make further efforts to reduce the intensity of the general population's exposure to environmental Cd.

Adult↗

PubMed1979

Potential antitumor agents. 29. Quantitative structure-activity relationships for the antileukemic bisquaternary ammonium heterocycles.

Quantitative relationships between physicochemical drug properties and antileukemic (L1210) efficacy have been examined for a series of bisquaternary ammonium heterocycles employing multiple variable regression analysis. Three measures of biologic response were examined: ILSmax, the percentage increase in mean life span of leukemic animals at the LD10 dose; D40, the drug dose necessary to provide 40% increase in life span; and CI (=LD 10/D40), the chemotherapeutic index. A cross correlation matrix between these three measures and the LD10 values demonstrates ILSmax and CI to be independent of toxicity. D40 is highly inversely correlated with LD10 and positively correlated with ILSmax, suggesting that this parameter measures a composite of both drug selectivity and toxicity. Superior regression equations resulted at all stages employing ILSmax as a measure of antitumor selectivity. Acceptable equations modeling LD10 could not be obtained. There was a parabolic relationship between agent lipophilic-hydrophilic balance, measured as chromatographic Rm values, and ILSmax. To reduce residual variance in the L1210 screening data, not accepted by this parabolic equation, measures of agent-DNA interaction were investigated as possible indices of site fit. Relative levels of drug-DNA interaction were obtained by spectrofluorimetric quantitation of drug displacement of DNA-bound ethidium. Addition to regression equations of agent C50 values for calf thymus DNA, those micromolar drug concentrations necessary to displace 50% of the ethidium bound to that DNA, provided a significant reduction in the screening data variance. C50 values for drug interactions with poly[d(A-T)] and poly[d(G-C)] were also investigated as possible indicators of drug selectivity towards different DNA sites. Marked differences were observed in the C50 values for the two synthetic nucleic acids, with those for calf thymus DNA and poly[d(G-C)] proving highly covariant. A regression equation containing a positive term in C50[poly[d(G-C)]] and a negative term in C50-[poly[d(A-T)]] provided the greatest acceptance of the variation in the biologic data. The term in C50[poly[d(A-T)]] is the single most important equation term, alone accounting for 35% of the variance in the data. This best equation provides both an adequate summary of the L1210 screening data for the 174 active compounds considered and a physical explanation for the antitumor selectivity for these agents. The major factor influencing antitumor selectivity in these drugs is their ability to distinguish alternating adenine-thymine sequences in DNA.

Animals↗

PubMed1975

Physical therapist assistant selection and academic success.

Assessment of a standardized test as one criterion for student admission to a physical therapist assistant program is made. Comparisons are made of ACT scores between the physical therapist assistant and associate degree nurse, and the physical therapist assistant and the practical nurse. A correlation matrix was used to analyze data with differences among the three groups determined by t test computation. This sample supports a positive correlation of ACT test scores with graduation grade point average. The means show no significant difference between the two associate degree programs and a significant difference between the associate degree programs and the practical nurse program.

Achievement↗

PubMed1997

Correlational structure of the MCMI-III personality disorder scales and comparisons with other data sets.

We examine the correlational structure of the personality disorder (PD) scales from the MCMI-III (Millon, 1994) among 614 college students. The correlation matrix from our nonclinical sample was highly similar to the clinical sample matrices reported by Millon (1994). Further analyses revealed that the correlation matrices from a variety of MCMI data sets are generally similar to one another, but are only moderately similar to PD correlation matrices based on other assessment techniques. PD correlation matrices based on different assessment techniques are generally not very similar to one another. Two-, 3-, and 4-factor solutions for the MCMI-III PD scales are reported and provide a framework for integrating apparently conflicting findings from previous work. The 4-factor solution was most meaningful and was consistent with the 5-factor model of PD.

Adolescent↗

PubMed1984

Growth parameters in normal fetuses.

A total of 14 linear measurements, seven ratios of linear measurements, and the weights of eight organs were taken from 100 normal fetuses. The fetuses had been therapeutically aborted between 11 and 19 weeks of gestational age by prostaglandin induction or hysterotomy. Measurements were obtained from at least five fetuses for each week of development age. A correlation matrix was calculated in order to identify those variables that showed a significant relationship with each other and with total body measurements. Significant correlations were obtained between crown-rump length and the following: head circumference, femur length, and humerus length. These three measurements were also significantly correlated with body weight. First-order regression equations were produced for these significantly correlated variables. This information can be used to estimate fetal growth even when the fetus is incomplete.

Anthropometry↗

PubMed1998

Relationships among multiple task asymmetries. II. A large-sample factor analysis.

Samples from published and unpublished factor analytic studies of multiple task asymmetry are combined to produce a large-sample factor analysis of 10 measures, prescreened for significant asymmetry and acceptable reliability, from 9 lateralized tasks. A full correlational matrix is presented, with task pairings having sample sizes ranging from 103 to 479 (mean N = 290). Both significant positive and significant negative correlations between measures are found. Extraction and oblique rotation of five factors fails to reveal any evidence of a global relationship among lateral difference measures, and principal-components analysis likewise fails to reveal a component to which all measures correlate positively. However, evidence for local structure is found. Results are interpreted in terms of dissociable hemispheric processes, and consideration is given of the possible existence of modality-specific characteristic perceptual asymmetry and of single versus multiple determination of lateral differences.

Adult↗

PubMed1981

Principal components analysis of sources of variability in retinal ganglion cell responses.

An approach to the functional organization of retinal ganglion cell processing in terms of correlation matrices (Levine and Shefner, 1975; 1977a, b; Shefner and Levine, 1979) is extended by applying Principal Components Analysis. This analysis reduces each correlation matrix to a few components which are implicit in the data. The component loadings describe properties of the system in terms of loadings (correlations) of time bins on the underlying components. Each component is identified by the experimental conditions associated with the highest loadings. Mixed conditions are quantitatively interpreted as weighted contributions from the various identified components. This has led to new interpretations of existing data. Several properties of ganglion cell inputs are analyzed in this manner, including ON and OFF processes, center and surround mechanisms, rod and cone inputs, and spatially distinct areas within the receptive field center. Although the details vary, generally one of the components is highly associated with ON processes and the other with OFF and/or MAINTAINED processes. several advantages may be realized through the use of Principal Components Analysis: (1) all of the data contribute to the analysis, (2) the number and relative importance of contributing processes may be assessed, (3) the relative contribution of underlying processes to mixed responses may be assessed, and (4) the most parsimonious representation of the data is obtained.

Animals↗

PubMed1988

Dental crowding and its relationship to mesiodistal crown diameters and arch dimensions.

An investigation was carried out to determine the correlation among cumulative mesiodistal crown widths, arch dimensions, and the degree of primary dental arch crowding. Two different ethnic groups were studied--namely, indigenous British and Pakistani immigrant groups--to determine whether similar correlations existed as part of a larger study of ethnic comparisons. Correlation matrix computation and multiple regression analysis were among the tests used. The results showed that in both ethnic groups there were very significant correlations between certain arch dimensions and the degree of crowding. There was no significant correlation between cumulative mesiodistal crown widths and dental crowding when considered in isolation. In combination with the other parameters, however, cumulative mesiodistal crown widths contributed significantly to the overall regression equation. This suggested a complex interrelationship among cumulative mesiodistal crown widths, the various arch dimensions, and primary dental crowding.

Adolescent↗

PubMed2005

Optimizing principal components analysis of event-related potentials: matrix type, factor loading weighting, extraction, and rotations.

OBJECTIVE: Given conflicting recommendations in the literature, this report seeks to present a standard protocol for applying principal components analysis (PCA) to event-related potential (ERP) datasets. METHODS: The effects of a covariance versus a correlation matrix, Kaiser normalization vs. covariance loadings, truncated versus unrestricted solutions, and Varimax versus Promax rotations were tested on 100 simulation datasets. Also, whether the effects of these parameters are mediated by component size was examined. RESULTS: Parameters were evaluated according to time course reconstruction, source localization results, and misallocation of ANOVA effects. Correlation matrices resulted in dramatic misallocation of variance. The Promax rotation yielded much more accurate results than Varimax rotation. Covariance loadings were inferior to Kaiser Normalization and unweighted loadings. CONCLUSIONS: Based on the current simulation of two components, the evidence supports the use of a covariance matrix, Kaiser normalization, and Promax rotation. When these parameters are used, unrestricted solutions did not materially improve the results. We argue against their use. Results also suggest that optimized PCA procedures can measurably improve source localization results. SIGNIFICANCE: Continued development of PCA procedures can improve the results when PCA is applied to ERP datasets.

Electroencephalography↗

PubMed2002

Water-soluble aerosol and visibility degradation in Hong Kong during autumn and early winter, 1998.

During the October-December 1998 period, 30 daily samples of size-separated airborne respirable suspended particulates (RSP) were collected at the quasi-rural Kadoorie Agricultural Research Centre (KARC) in central New Territories (NT), Hong Kong, Special Administrative Region (SAR). Results of analysis indicate that sulphate is the predominant water-soluble species, and that sulphate, nitrate and ammonium together contribute to most of the total water-soluble fine aerosol mass. An interesting result obtained through principal component analysis (PCA) following varimax rotation of the bivariate correlation matrix for water-soluble species is that the first component (PCl) is made up exclusively of SO4 and NH4 ions. The stoichiometric ratio and correlation coefficient between the two ions suggest that ammoniated sulphate compounds are the probable species responsible for the PCI. Further, the use of a linear multivariate visibility model which accommodates the effect of relative humidity (RH) shows that SO4 and NH4 are the only anions important in visibility degradation. It is found that SO4 in aerosol at the KARC can be used to predict the visual range (or extinction coefficient) recorded from Kings Park, Kowloon, approximately 10 km away. This result suggests that SO4 (and possibly NH4) is, generally, likely to be of regional rather than of local origin. Further observations suggest that the model is most applicable to a moderate visual range, 10 km < R(v) < or = 20 km under a rather broad range of ambient relative humidity, 40% < RH < or = 80. However, this inference does not preclude the contributions to visibility degradation--mostly by absorption--by some of the water-insoluble aerosol constituents, including carbon, or the pollutant gas, NO2.

Aerosols↗

PubMed1982

Atomic absorption spectrometric evidence of relationships between some cationic elements in human dentine.

Dentine samples were prepared from 123 permanent teeth and Co, Cu, Mg, Mn, Ni, Pb, Sr and Zn concentrations were determined with an atomic absorption spectrophotometer. Relations between the cations were evaluated using the correlation matrix and multiple linear regression analysis. When the simultaneous variation of the concentrations of all determined elements was taken into consideration, the following statistically significant positive correlations were found: Cu-Mn, Mn-Co, Ni-Mn and Sr-Ni. A weaker correlation was obtained between Ni and Mg and between Ni and Pb. The only negative correlation was between Sr and Pb, but the explanation percentage in the regression model was low. The results indicated that the chemically and physically related elements Co, Cu, Mn and Ni formed positive correlations. Sr-Ni and Mn-Cu relationships were similar to those reported for human cancellous bone.

Adolescent↗

PubMed1991

Systemic effects of inflammation in bronchiectasis.

A group of bronchiectatic subjects in the clinically stable state were studied for systemic evidence of inflammation. The following parameters were evaluated: body weight, serum albumin, serum globulin, serum alpha 1-antitrypsin (alpha 1 AT) and peripheral white cell count. For serum albumin and globulin, comparison was made between subjects with bronchiectasis and control subjects with no known pulmonary disease matched for sex and age, and for serum alpha 1 AT and peripheral white cell count, matched for smoking habit as well. The bronchiectatic subjects showed systemic effects of inflammation as indicated by lower body weight and serum albumin (P less than 0.01), higher serum globulin (P less than 0.001), serum alpha 1 AT (P less than 0.05) and total leucocyte count (P less than 0.05). Differential white cell count showed that the elevation was distributed in most cell types. Correlation matrix was done for the above systemic parameters and indices of airway inflammation including sputum volume, purulence, and polymorph count and FEV1. There was an inverse correlation between total peripheral WBC count and FEV1 in percentage of predicted (P less than 0.01), and a positive correlation between sputum purulence and sputum polymorph score (P less than 0.05). This suggests that host peripheral leucocyte response may be a factor in the determination of lung function.

Adolescent↗