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PubMed1999

Evaluation of data produced by optode arrays under flow injection analysis (FIA) conditions using a partial least squares method (PLS2).

Transient diffuse reflectance spectra in the visible wavelength region from an enzyme optode were evaluated to determine artificial mixtures consisting of penicillin and ampicillin simultaneously. In order to achieve a discrimination of the samples the optode operated at two different working pH values. Using an appropriate FIA modus a linear range in the increase and decrease of the time-dependent signal was registered which could be easily fitted by means of ordinary linear regression. In this way characteristic static and dynamic features of the enzyme catalyzed reaction could be extracted for the evaluation by partial least-squares (PLS). The pre-processed raw data were differently weighted and the optimal number of primary factors was each selected by full cross validation. The interpretation of the spectral loadings and the correlation matrix identifies redundant variables resulting in a model with an optimal number of variables. The results obtained with this model show that the straightforward linear regression can be a sufficient approach to avoid the introduction of systematic errors in on-line pre-processing of data.

Ampicillin↗

PubMed1998

Depression and dependency: distinct or overlapping constructs?

BACKGROUND: Previous research has found a significant positive relationship between dependency and level of depression. The aim of the present study, using factor analysis method, is to test the hypothesis that dependency and depression constitute distinct dimensions. METHODS: In a sample of 202 university students, a correlation matrix comprising items from both the Interpersonal Dependency Inventory and the abridged form of the Beck Depression Inventory was analysed using a principal components analysis followed by an orthogonal varimax rotation. RESULTS: Evidence for a four-factor solution was found with almost no overlap of the significant factor loadings for the items from each scale, and with the factors corresponding closely with their respective construct. CONCLUSION: The findings support the view that depression and dependency constitute different constructs. LIMITATION: The results must be confirmed on clinical and heterogeneous nonclinical samples. CLINICAL RELEVANCE: The independency between depression and dependency could lead to different therapeutic strategies notably in 'socially dependent' type of depression.

Adult↗

PubMed2000

Dimensions of maternal behaviour characteristics in domestic and wildxdomestic crossbred sows.

We examined the maternal behaviour of seven domestic and seven wildxdomestic primiparous sows during 10 days post partum to investigate two questions: (1) Did maternal behaviour change during domestication? (2) Can the interindividual variability of maternal behaviour be subsumed into a few dimensions of maternal temperament? We recorded: (a) willingness to leave the nest for food on Day 2; (b) reaction to a playback of squeezed piglet distress vocalisation on Day 2; (c) spontaneous nursing behaviour and spontaneous lying-down behaviour on Day 5 (from an overnight video recording); (d) reactions to playbacks of various piglet distress vocalisations on Day 6 and (e) reactions to a human in the 'nest' with piglets on Day 9. Moreover, data on baseline cortisol saliva concentration and its increase during a brief transportation period and novel environment challenge at the age of 5 months were available. Crossbred sows did not differ from domestic ones in any aspect of maternal behaviour except for a higher tendency to terminate final massage during nursings and a higher frequency of changing posture from lying to standing and back during the night. Factor analysis (based on correlation matrix of 11 behaviour and cortisol variables calculated for all 14 sows after removing the effect of breed) indicated that 82% of the variability in the data could be explained by three factors: first, 'calmness' on which low night time frequency of major posture changes, carefulness of lying-down behaviour and high propensity to remain in nursing position after milk ejection loaded positively while cortisol concentrations during challenge loaded negatively; second, 'protectiveness' with high loadings of the reaction scores to the playbacks of piglet distress calls and the human presence near the piglets; and third, 'nursing activity' which was strongly positively associated with nursing frequency, and negatively with the proportion of nutritive nursings and baseline cortisol values. The results indicate that most aspects of pig maternal behaviour have not been significantly changed by domestication and that substantial variability in maternal behaviour exists between sows, perhaps in the form of several behaviour characteristics which encompass both behaviour and endocrine profiles of the sows.

Journal Article↗

PubMed2001

Dimension reduction and source identification for multispecies groundwater contamination.

Assessment of chemical contamination at large industrial complexes with long and sometimes unknown histories of operation represents a challenging environmental problem. The spatial and temporal complexity of the contaminant may be due to changes in production processes, differences in the chemical transport, and the physical heterogeneity of the soil and aquifer materials. Traditional mapping techniques are of limited value for sites where dozens of chemicals with diverse transport characteristics may be scattered over large spatial areas without documentation of disposal histories. In this context, a site with a long and largely undocumented disposal history of shallow groundwater contamination is examined using principal component analysis (PCA). The dominant chemical groups and chemical "modes" at the site were identified. PCA results indicate that five primary and three transition chemical groups can be identified in the space of the first three eigenvectors of the correlation matrix, which account for 61% of the total variance of the data. These groups represent a significant reduction in the dimension of the original data (116 chemicals). It is shown that each group represents a class of chemicals with similar chemo-dynamic properties and/or environmental response. Finally, the groups are mapped back onto the site map to infer delineation of contaminant source areas for each class of compounds. The approach serves as a preliminary step in subsurface characterization, and a data reduction strategy for source identification, subsurface modeling and remediation planning.

Environmental Monitoring↗

PubMed1997

The comparability and reliability of five health-state valuation methods.

The objective of the study was to consider five methods for valuing health states with respect to their comparability (convergent validity, value functions) and reliability. Valuation tasks were performed by 104 student volunteers using five frequently used valuation methods: standard gamble (SG), time trade-off (TTO), rating scale (RS), willingness-to-pay (WTP) and the paired comparisons method (PC). Throughout the study, the EuroQol classification system was used to construct 13 health-state descriptions. Validity was investigated using the multitrait-multimethod (MTMM) methodology. The extent to which results of one method could be predicted by another was examined by transformations. Reliability of the methods was studied parametrically with Generalisability Theory (an ANOVA extension), as well as non-parametrically. Mean values for SG were slightly higher than TTO values. The RS could be distinguished from the other methods. After a simple power transformation, the RS values were found to be close to SG and TTO. Mean values of WTP were linearly related to SG and TTO, except at the extremes of the scale. However, the reliability of WTP was low and the number of inconsistencies substantial. Valuations made by the RS proved to be the most reliable. Paired comparisons did not provide stable results. In conclusion, the results of the parametric transformation function between RS and SG/TTO provide evidence to justify the current use of RS (with transformations) not only for reasons of feasibility and reliability but also for reasons of comparability. A definite judgement on PC requires data of a complete design. Due to the specific structure of the correlation matrix which is inherent in valuing health states, we believe that full MTMM is not applicable for the standard analysis of health-state valuations.

Adult↗

PubMed2000

Cadaveric donotransplantation: nurses' attitudes, knowledge and behaviour.

Human organ transplantation is an important treatment for certain medical conditions, and for irreversible organ failure. There is a shortfall in the number of organs required for transplantation. The close and continuous proximity of nurses to potential donors and their families make them critical links in the organ donation process. Therefore, success in organ procurement may depend on nurses' awareness and integration of knowledge about donotransplantation (the process of organ/tissue donation and transplantation). Postal questionnaires were distributed throughout the United Kingdom (UK) to 2465 registered nurses, to assess their personal attitudes, knowledge and behaviour regarding cadaveric donotransplantation. One thousand, three hundred and thirty-three questionnaires were returned, a response rate of 54%. Overall, nurses held positive attitudes to donotransplantation, with 78% agreeing with organ donation and only 10% clearly being opposed. However, nurses were found to share ambivalent attitudes of altruism and fear which appear to surround decisions about donation. Factor analysis was used to further explore nurses' attitude structure. Six factors were confirmed providing a non-significant likelihood ratio fit (P = 0.468) and a well reproduced correlation matrix. The factors related to: (1) the value and contribution made by donotransplantation; (2) the unique idea of having another's tissue in one's own body; (3) the importance of organ donation; (4) the individual's moral, and nurses' professional rejection of the responsibility for organ/tissue donation; (5) the post-mortem mutilation of the body; and, (6) the potential distress donation may cause a bereaved family. Comparisons were made between certain of nurses' specialist groups and significant differences were found. Comparisons of factor scores between certain specialist groups or other strata were assessed by analysis of variance. Nurses working in renal units were significantly more in favour of donotransplantation than any other group of nurses.

Cadaver↗

PubMed2003

Artificial neural networks (ANNs) and modeling of powder flow.

Effects of micromeritic properties (bulk, tapped and particle density, particle size and shape) on the flow rate through circular orifices are investigated, for three pharmaceutical excipients (Lactose, Emcompress and Starch) separated in four sieve fractions, and are modeled with the help of artificial neural networks (ANNs). Eight variables were selected as inputs and correlated by applying the Spearman product-moment correlation matrix and the visual component planes of trained Self-Organizing Maps (SOMs). Back-propagation feed-forward ANN with six hidden units in a single hidden layer was selected for modeling experimental data and its predictions were compared with those of the flow equation proposed by. It was found that SOMs are efficient for the identification of co-linearity in the input variables and the ANN is superior to the flow equation since it does not require separate regression for each excipient and its predictive ability is higher. Besides the orifice diameter, most influential and important variable was the difference between tapped and bulk density. From the pruned ANN an approximate non-linear model was extracted, which describes powder flow rate in terms of the four network's input variables of the greatest predictive importance or saliency (difference between tapped and bulk density (x(2)), orifice diameter (x(3)), circle equivalent particle diameter (x(4)) and particle density [equation in text].

Excipients↗

PubMed1985

Methionine intolerance: a possible risk factor for coronary artery disease.

Homocystinuria, an inherited disorder associated with premature atherosclerosis, represents a severe form of methionine intolerance. To analyze the importance of milder forms of methionine intolerance in the genesis of vascular disease, the relation between provokable methionine intolerance and coronary artery disease was investigated. In a group of 138 men, aged 31 to 65 years (mean 53), referred for cardiac catheterization, plasma homocystine was measured before and 6 hours after an oral l-methionine load (0.1 g/kg). Thirty-nine subjects found to have normal coronary arteries had a mean post-load plasma homocystine level of 0.59 +/- 0.37 mumol/liter. A criterion at the 95th percentile (1.64 SD above the mean) was selected and applied to the remaining 99 subjects with coronary artery disease (0.70 +/- 0.68 mumol/liter). Sixteen (16%) of 99 subjects with coronary artery disease exceeded this level as compared with 1 (2%) of 39 subjects without coronary artery disease (p less than 0.04). The risk of coronary artery disease in men with provokable methionine intolerance was increased sevenfold as estimated by the odds ratio. By correlation matrix and multivariate regression analyses, provokable homocystinemia was predictive of coronary artery disease and was independent of tobacco smoking, hypertension, diabetes mellitus, serum cholesterol and age. It is proposed that men with mild methionine intolerance exposed to the high methionine content of the Western diet may develop intermittent homocystinemia and thus may be at greater risk for the development of coronary artery disease.

Adult↗

PubMed1997

Characteristic Functions and Process Identification by Neural Networks.

Principal component analysis (PCA) algorithms use neural networks to extract the eigenvectors of the correlation matrix from the data. However, if the process is non-Gaussian, PCA algorithms or their higher order generalisations provide only incomplete or misleading information on the statistical properties of the data. To handle such situations we propose neural network algorithms, with an hybrid (supervised and unsupervised) learning scheme, which constructs the characteristic function of the probability distribution and the transition functions of the stochastic process. Illustrative examples are presented, which include Cauchy and Lévy-type processes.

Journal Article↗

PubMed2001

Geophysical natural gamma-ray well logging and spectrometric signatures of south AL-Abter phosphatic deposits in Syria.

A combination of several exploration techniques was carried out in AL-Abter region, aiming at outlining the main characteristics of the phosphatic layers in this region. The techniques used in this research are natural 7-ray well logging, gamma and alpha-spectrometry. It is shown that uranium concentrations in the samples taken from the wells studied vary between 42.8 and 112.5 ppm with a standard deviation of 15.2 ppm. The P2O5 content varies between 20.5% and 28.31% with a standard deviation of 3.11% and the radioactive intensities vary between 150 and 275 counts per second (cps) with a standard deviation of 31 cps. The ratio of 234U/238U in the analyzed samples indicates that the study region is in radioactive equilibrium. The affinity of uranium and P2O5 to some trace elements, such as V, Sr, Cu and Ni has been verified through studying the correlation matrix of these elements.

Journal Article↗

PubMed2002

Reliability and validity of the youth asset survey (YAS).

PURPOSE: To describe the construction of a survey that was developed to measure youth assets. The paper details the ten youth developmental assets measures within the survey, including the psychometric properties of those measures derived from factor analysis and reliability testing. METHODS: Three studies were conducted, including a study of 1,350 randomly selected youth (mean age = 15.4 years; 52% female; 47% white, 22% black, 19% Hispanic, 10% Native American), using in-person interviews, to develop an asset instrument tool. Factor analysis was performed on a correlation matrix, using principal axis factoring, and varimax rotation. The criteria were set to extract eight factors. RESULTS: The eight factors extracted represented six developmental assets as originally defined, including Family Communication, Peer Role Models, Future Aspirations, Responsible Choices, Community Involvement, and Non-Parental Role Models. One asset (Constructive Use of Time) was split into two specific assets: groups/sports and religious time. Two assets did not form factors (Good Health Practices [exercise/nutrition] and Cultural Respect) and were defined as one-item assets. All factor loading scores were.40 or higher and all Cronbach alphas were.60 or higher. CONCLUSIONS: Factor analyses suggest that the constructs are reliable measures of youth developmental assets. The psychometrically sound asset measures presented here will provide scientists with valid and reliable instruments to assess and compare the prevalence of youth assets across populations and to investigate potential relationships between youth assets and other outcomes, such as youth risk behaviors.

Adolescent↗

PubMed2003

Religiosity and its relation to blood pressure among selected Kuwaitis.

This study examines the relationship between blood pressure and the religious practices of Kuwaitis as members of a Muslim society. Religious variables were measured via a sociocultural questionnaire. Blood pressure measurements were taken with a sphygmomanometer. Non-opportunistic samples were taken from 223 Kuwaitis. The difference in religious commitment between Muslim Sunnis and Muslim Shiites was examined using a t-test. Matrix correlation was used to examine the relationship between religious commitment and some other variables. Multiple regression was conducted to determine the effect of religiosity on blood pressure, as well as statistically controlling for other variables such as body mass index, socioeconomic status, smoking, gender and age. It was found that both systolic and diastolic blood pressure were affected by religious commitment and religious activities

Adolescent↗

PubMed1998

The dimensional structure of first episode psychosis: an exploratory factor analysis.

BACKGROUND: Recent research has focused upon the subdiagnostic level in an effort to derive more valid domains of psychotic disorder. This has led to the influential positive-negative dichotomy in schizophrenia being superseded by a three-syndrome model. The strategy of looking for syndromes within poorly validated diagnostic categories, such as schizophrenia, has limitations, particularly since it originated in, and has been largely restricted to, the more chronic subsamples. METHOD: A representative sample of first episode psychosis (N = 509), which includes the full spectrum of functional psychosis, was utilized to re-examine the dimensional structure of functional psychosis from first principles. Patients were assessed with the Royal Park Multidiagnostic Instrument for Psychosis (MIP), a comprehensive procedure that documents the psychopathology of the first episode in a clinically valid manner. RESULTS: Principal axis factor analysis was carried out on the tetrachoric correlation matrix of 92 core psychopathological items. A robust and clinically valid four-factor solution was obtained, comprising depression, mania and only two other factors. The first was a Bleulerian blend of negative symptoms, catatonic/motor symptoms and disorganization. The second was a combination of Schneiderian first rank symptoms, and other hallucinations and delusions. The data thus failed to support the three-syndrome model for non-affective symptoms in this population. A six-factor solution, although partially consistent with other studies, represented a more complex and confusing elaboration of the more clinically valid four-factor solution. CONCLUSIONS: The findings have implications for the conceptualization of early psychosis, which need to be explored further in validation studies.

Adult↗

PubMed1999

Averaging dependent effect sizes in meta-analysis: a cautionary note about procedures.

When a primary study includes several indicators of the same construct, the usual strategy to meta-analytically integrate the multiple effect sizes is to average them within the study. In this paper, the numerical and conceptual differences among three procedures for averaging dependent effect sizes are shown. The procedures are the simple arithmetic mean, the Hedges and Olkin (1985) procedure, and the Rosenthal and Rubin (1986) procedure. Whereas the simple arithmetic mean ignores the dependence among effect sizes, both the procedures by Hedges and Olkin and Rosenthal and Rubin take into account the correlational structure of the effect sizes, although in a different way. Rosenthal and Rubin's procedure provides the effect size for a single composite variable made up of the multiple effect sizes, whereas Hedges and Olkin's procedure presents an effect size estimate of the standard variable. The three procedures were applied to 54 conditions, where the magnitude and homogeneity of both effect sizes and correlation matrix among effect sizes were manipulated. Rosenthal and Rubin's procedure showed the highest estimates, followed by the simple mean, and the Hedges and Olkin procedure, this last having the lowest estimates. These differences are not trivial in a meta-analysis, where the aims must guide the selection of one of the procedures.

Data Interpretation, Statistical↗

PubMedDate not supplied

A method for correlations analysis of coordinates: applications for molecular conformations.

We describe a new method to analyze multiple correlations between subsets of coordinates that represent a sample. The correlation is established only between specific regions of interest at the coordinates. First, the region(s) of interest are selected at each molecular coordinate. Next, a correlation matrix is constructed for the selected regions. The matrix is subject to further analysis, illuminating the multidimensional structural characteristics that exist in the conformational space. The method's abilities are demonstrated in several examples: it is used to analyze the conformational space of complex molecules, it is successfully applied to compare related conformational spaces, and it is used to analyze a diverse set of protein folding trajectories.

Amino Acid Sequence↗

PubMed1983

Selection of test series by a modified multidimensional mapping method.

Maintaining a realistic minimum distance between compounds in a defined multidimensional parameter space ensures well-spread sets of parameter values. It has been suggested, however, that the use of this multidimensional mapping method may lead to series of compounds with high multicollinearities of parameter values. An alternative method, multidimensional mapping by distance and determinant, is discussed here. This method maximizes the determinant of the interparameter correlation matrix as well as maintaining the minimum distance criterion. Its performance is compared with other methods, and it is shown that collinearities may be overcome or maintained at low levels when this method is used.

Molecular Conformation↗

PubMed1999

Distinguishing between quality of life and health status in quality of life research: a meta-analysis.

Despite the increasing acceptance of quality of life (QOL) as a critical endpoint in medical research, there is little consensus regarding the definition of this construct or how it differs from perceived health status. The objective of this analysis was to understand how patients make determinations of QOL and whether QOL can be differentiated from health status. We conducted a meta-analysis of the relationships among two constructs (QOL and perceived health status) and three functioning domains (mental, physical, and social functioning) in 12 chronic disease studies. Instruments used in these studies included the RAND-36, MOS SF-20, EORTC QLQ-30, MILQ and MQOL-HIV. A single, synthesized correlation matrix combining the data from all 12 studies was estimated by generalized least squares. The synthesized matrix was then used to estimate structural equation models. The meta-analysis results indicate that, from the perspective of patients, QOL and health status are distinct constructs. When rating QOL, patients give greater emphasis to mental health than to physical functioning. This pattern is reversed for appraisals of health status, for which physical functioning is more important than mental health. Social functioning did not have a major impact on either construct. We conclude that quality of life and health status are distinct constructs, and that the two terms should not be used interchangeably. Many prominent health status instruments, including utility-based questionnaires and health perception indexes, may be inappropriate for measuring QOL. Evaluations of the effectiveness of medical treatment may differ depending on whether QOL or health status is the study outcome.

Health Status↗

PubMed2000

Oocyte morphology and early zygote cleavage does not appear to be related to intrafollicular concentrations of inhibin-A or -B.

PURPOSE: The aim was to investigate the relationship of intrafollicular inhibin dimers A and B with human oocyte morphology and subsequent embryo potential. METHODS: Sixty-eight oocytes were isolated from 31 women undertaking intracytoplasmic sperm injection (ICSI). Estradiol, progesterone, testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, sex hormone-binding globulin, inhibin-A and inhibin-B was assayed in corresponding follicular fluid. RESULTS: The mean (+/- SD) concentration for inhibin-A was 9.7 +/- 9.8 ng/ml (range, 1.1-60.0 ng/ml) and for inhibin-B was 269.4 +/- 185.2 ng/ml (range, 33.1-811.0 ng/ml). In a correlation matrix there were no marked relationships (r < 0.556) between inhibin and steroid or gonadotropin concentrations. Similarly, when inhibin concentrations were divided according to whether the oocytes had mature or immature cumulous complexes, were viable or necrotic, were meiotically immature or mature, became fertilized or not, or had different embryo gradings after cleavage, no statistically significant difference could be seen between groupings. CONCLUSIONS: Because the range of values was large and the data often skewed, neither inhibin dimer has discriminatory power to reflect the potential of the oocyte.

Adult↗