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At least 325 records · Page 18Linked to original sources

PubMed2000

Heroin impurity profiling. A harmonization study for retrospective comparisons.

Three laboratories present a harmonised system for the retrospective comparison of south west Asian heroin. It consists of an improved gas chromatographic (GC) profiling method and a computerised data retrieval. The investigations of the GC were necessary with a view to improve the reproducibility of the system. The necessity of a strict quality control is emphasized. The peaks of the GC profile were investigated for abundance, intensity, GC behaviour (reproducibility) and correlations; 16 of them were selected for describing the heroin profile in the database. The results from intra-lab profile comparisons are reported. The reproducibility of the analysis was good and the variation between the samples was large, thus, allowing conclusions with a high degree of certainty. The criteria of similarity were defined. The system is successfully running in all three labs. In connection with inter-laboratory comparison, the aspects of method harmonisation and standardisation are discussed. It appeared that the GC method is a very subtile one, urging for a strict standardisation between the three labs. Despite a long cooperation between three well-equipped and experienced labs, a more or less serious loss of reproducibility was noticed in the inter-lab results in comparison with the intra-lab results. The loss could for the greater part be attributed to the (limits of the) GC technique; a number of compounds, necessary for making the discrimination between samples, showed difficult chromatographic behaviour, leading to insufficient inter-lab reproducibility. Using the actual variables, improvements in performance can hardly be expected in the near future. The loss of reproducibilty implies that the number of false positive matches in a database search increases. This may strongly reduce the value of a relatively large, international database. The study shows that so far, the best option for international comparison is the analysis in a central laboratory. The idea of local determination at a large number of national labs and the use of a common database is not a realistic aim for this type of analysis.

Chromatography, Gas↗

PubMed1999

Statistical issues encountered in the comparison of health-related quality of life in diseased patients to published general population norms: problems and solutions.

The objectives of this study were (1) to illustrate the statistical problems encountered when comparing health-related quality of life (HRQL) measured by the Medical Outcome Study Short Form-36 (SF-36) in a diseased group to general population norms, and (2) to define age- and gender-standardized dichotomous indicator variables for each health concept and show that these indicator variables facilitate comparisons between the diseased sample and the general population. Our "diseased" group consisted of 136 sequentially consenting patients referred to the syncope clinic for assessment and treatment. Participants completed the SF-36 questionnaire before undergoing diagnostic testing. General population norms for the SF-36 are available from the responses of 2474 participants in the National Survey of Functional Health Status, conducted in 1990 in the United States. Comparison of the SF-36 in a diseased sample with general population norms is difficult, owing to skewed and unusual distributions in both groups. In addition, making comparisons within age and gender strata is difficult if the within strata sample size is small. We propose a dichotomous indicator variable for each health concept that classifies an individual as having impaired health if he or she scored lower than the 25th percentile for the appropriate age and gender general population strata. By definition, the prevalence of impaired health in the general population is 25% for all eight health concepts. Comparison between the eight health-concept variables is easy because the population norm is the same for each of them. These indicator variables are age and gender adjusted, so that even if the sample did not have the age and gender distribution as the general population, comparisons can still be made with the value of 25.

Activities of Daily Living↗

PubMedDate not supplied

Results from APMP comparisons on radioactivity measurements of 58Co, 88Y and 166mHo.

International comparisons on radioactivity measurements of 55Co, 88Y and 166mHo were carried out within the framework of the Asia-Pacific Metrology Programme. Radioactive sources were also sent to the International Reference System (SIR) at the Bureau International des Poids et Mesures (BIPM) in order to link the results of these regional comparisons to the BIPM key comparison-reference values. The arithmetic mean for the activity results of 166mHo was in good agreement with the SIR reference value, but some disagreements were found for 58Co and 88Y results. The mean values for 58Co and 88Y were both higher than the existing SIR values by about 1.5% and 0.9%, respectively. Although there were some disagreements, it was successfully demonstrated that these regional comparisons could be linked to other international key comparisons through the SIR. The present results were also evaluated to estimate a reasonable uncertainty level for each laboratory, which is very important in the establishment of an adequate traceability scheme for radioactivity standards.

Journal Article↗

PubMed1996

Comparison of receiver operating characteristic curves on the basis of optimal operating points.

RATIONALE AND OBJECTIVES: We developed a method of comparing receiver operating characteristic (ROC) curves on the basis of the utilities associated with their optimal operating points (OOPs). METHODS: OOPs were computed for paired ROC curves on the basis of isocost lines in ROC space with slopes ranging from 0.1 to 3.0. For each pair of OOPs corresponding to a single isocost slope, the difference in costs and the variance of this difference was computed. A sensitivity analysis was thus obtained for the difference between the two curves over a range of isocost slopes. Three published data sets were evaluated using this technique, as well as by comparisons of areas under the curves and of true-positive fractions at fixed false-positive fractions. RESULTS: The OOPs of paired ROC curves often occur at different false-positive fractions. Comparisons of ROC curves on the basis of OOPs may provide results that differ from comparisons of curves at a fixed false-positive fraction. CONCLUSION: ROC curves may be compared on the basis of utilities associated with their OOPs. This comparison of the optimal performance of two diagnostic tests may differ from conventional statistical comparisons.

Costs and Cost Analysis↗

PubMedDate not supplied

Compare-Conformer: a program for the rapid comparison of molecular conformers based on interatomic distances and torsion angles.

A computer program for comparison of the conformations of a number of related molecular structures is described. The comparisons are performed on either interatomic distances or torsion angles. The comparisons are accomplished on ordered pairs of distances or torsion angles, and the distance comparisons can be performed in a manner that allows permutation of the distance pairs being compared. The algorithm utilizes bit-string Boolean operations that allow the comparisons to be performed rapidly. The program should be useful for computer-assisted molecular modeling studies in which the viable conformers of bioactive analogues are compared in order to locate those conformers that place key substituents in the same spatial orientation.

Acetylcholine↗

PubMed1989

Intrapersonal and social comparison determinants of happiness: a range-frequency analysis.

Examined whether intrapersonal comparisons and social comparisons operate in similar ways to determine ratings of happiness. Events were varied to create positively and negatively skewed distributions. The events in each distribution were ascribed to either a single person or a group of people; Ss rated how happy they would feel if they experienced specific events within the distribution. Ratings for both intrapersonal and social comparisons were fit well by Parducci's (1984) range-frequency theory. Individual events received higher ratings when presented within the positively skewed context. Overall happiness, as measured by both the mean of the happiness ratings as well as direct ratings, was highest for the negatively skewed distributions. The effects of skewing were more pronounced for intrapersonal comparisons, but ratings were more closely defined by the range of experimental stimuli for social comparisons.

Adult↗

PubMed1994

Self-evaluation effects of interpersonal versus intergroup social comparison.

Two studies tested the prediction that the outcome of social comparison will differ depending on whether interpersonal or intergroup comparison processes have been engaged. Results of an experiment in which college student participants were assigned to membership in a minority or majority social category confirmed the predicted three-way interaction effect of in-group salience, target group membership, and upward-downward comparison on self-assessments of academic ability. Majority group members exhibited contrast effects in their self-ratings following exposure to a videotape of an in-group member displaying either very high or very low academic competence. Self-evaluations of minority group members revealed assimilation effects in response to in-group comparisons and contrast effects in response to out-group comparisons. In a second, follow-up experiment, this in-group assimilation effect was found to be dependent on intergroup contrast.

Adult↗

PubMed2001

I, we, and the effects of others on me: how self-construal level moderates social comparison effects.

In 5 studies, the authors investigate the impact of self-activation on the occurrence and direction of social comparison effects. They show that self-evaluative comparison effects are more likely to occur when self-related cognitions are made cognitively accessible. Contrast occurs when personal self-construals ("I") are accessible, whereas assimilation occurs when social self-construals ("we") are activated. These effects of self-construal activation are similar to the impact of self-unrelated information processing styles that are often associated with personal and social self-accessibility (i.e., differentiation and integration mind-sets). However, whereas self-construal activation elicits self-serving social comparisons, activation of self-unrelated processing styles results in non-self-serving social comparison effects. Implications of these results for understanding the cognitive processes underlying social comparison effects are discussed.

Adolescent↗

PubMed2002

The influence of individual versus aggregate social comparison and the presence of others on self-evaluations.

In 5 studies, the authors investigated the effects of comparison with an individual versus comparison with the statistical average on self-evaluations of performance and ability. In Studies 1 and 2, participants took a test of lie detection ability and were provided with the average score and the score of an individual coactor. Both types of feedback significantly affected self-evaluations of performance, but only comparison with the coactor significantly affected self-evaluations of ability. Studies 3 and 4 demonstrated that the presence of a coactor moderated the effect of aggregate social comparison on self-evaluations of ability. The results provide preliminary support for the contention that minimizing the impact of comparison with the average is a self-serving strategy that is facilitated by the presence of others.

Adolescent↗

PubMed2003

Comparison processes in social judgment: mechanisms and consequences.

This article proposes an informational perspective on comparison consequences in social judgment. It is argued that to understand the variable consequences of comparison, one has to examine what target knowledge is activated during the comparison process. These informational underpinnings are conceptualized in a selective accessibility model that distinguishes 2 fundamental comparison processes. Similarity testing selectively makes accessible knowledge indicating target-standard similarity, whereas dissimilarity testing selectively makes accessible knowledge indicating target-standard dissimilarity. These respective subsets of target knowledge build the basis for subsequent target evaluations, so that similarity testing typically leads to assimilation whereas dissimilarity testing typically leads to contrast. The model is proposed as a unifying conceptual framework that integrates diverse findings on comparison consequences in social judgment.

Decision Making↗

PubMed2004

The effect of social comparison information on the life satisfaction of frail older persons.

In this study, the authors examined the effects of social comparison on the life satisfaction of 455 community-dwelling older persons. These older persons were confronted with a fictitious interview with either an upward or a downward target. After downward comparison, older persons felt more satisfied with their lives than after upward comparison, especially those who had higher levels of frailty. These effects were only found with lower levels of identification. Apparently, downward comparison only serves its self-enhancing function on life satisfaction among frail older persons when they perceive the comparison target as different from themselves.

Aged↗

PubMed1999

Comparison of two carbon analysis methods for monitoring diesel particulate levels in mines.

Two carbon analysis methods are currently being applied to the occupational monitoring of diesel particulate matter. Both methods are based on thermal techniques for the determination of organic and elemental carbon. In Germany, method ZH 1/120.44 has been published. This method, or a variation of it, is being used for compliance measurements in several European countries, and a Comité Européen de Normalization Working Group was formed recently to address the establishment of a European measurement standard. In the USA, a 'thermal-optical' method has been published as Method 5040 by the National Institute for Occupational Safety and Health. As with ZH 1/120.44, organic and elemental carbon are determined through temperature and atmosphere control, but different instrumentation and analysis conditions are used. Although the two methods are similar in principle, they gave statistically different results in a previous interlaboratory comparison. Because different instruments and operating conditions are used, between-method differences can be expected in some cases. Reasonable agreement is expected when the sample contains no other (i.e., non-diesel) sources of carbonaceous particulate and the organic fraction is essentially removed below about 500 degrees C. Airborne particulate samples from some mines may meet these criteria. Comparison data on samples from mines are important because the methods are being applied in this workplace for occupational monitoring and epidemiological studies. In this paper, results of a recent comparison on samples collected in a Canadian mine are reported. As seen in a previous comparison, there was good agreement between the total carbon results found by the two methods, with ZH 1/120.44 giving about 6% less carbon than Method 5040. Differences in the organic and elemental carbon results were again seen, but they were much smaller than those obtained in the previous comparison. The relatively small differences in the split between organic and elemental carbon are attributed to the different thermal programs used.

Air Pollution, Indoor↗

PubMed1985

Simultaneous comparison of three protein sequences.

Currently there are several computer algorithms available for aligning two biological sequences. When more than two sequences are to be aligned, however, pairwise comparisons using these methods rarely lead to a consistent alignment of the sequences. One obvious solution to this problem is to compare all the sequences simultaneously. Here we present an algorithm for the simultaneous comparison of three biological sequences. The algorithm is an extension of the method developed by S. B. Needleman and C. D. Wunsch, but it decreases the almost prohibitively long computing time required by a direct naive extension to a practical level: it takes time proportional to the cube of the mean sequence length, in comparison to the fifth power time taken by the direct extension. Simultaneous comparison not only gives a consistent alignment of the three sequences, but it could also reveal homologous residues in the sequences that might be overlooked by the pairwise comparisons. As an example of the application of the algorithm, three copper-containing proteins, plastocyanin, stellacyanin, and cucumber basic blue protein, are compared.

Amino Acid Sequence↗

PubMed2002

Young children's learning of size comparison strategies: effect of origami exercises.

The authors examined the process of change in size comparison strategies among preschool-age children. Twelve 5- and 6-year-old children were provided with origami exercises and size comparison tasks for 5 days consecutively, and another twelve 5- and 6-year-old children received size comparison tasks only. Children's strategies for the size comparison tasks were analyzed in terms of placement and adjustment. In contrast with the children in the control condition, the children who were provided with exercises in origami increased their use of superimposition and adjustment strategies by 2 dimensions across the 5 days. The authors argue that origami exercises helped the children connect their implicit understanding of relative size with the use of more effective strategies for size comparison.

Child↗

PubMed1996

The underestimated role of temporal comparison: a test of the life-span model.

The assumption of the life-span model (Suls & Mullen 1982)--that age affects the way people make comparisons--was tested. Three groups of participants in England--young adults (18-39 years old; n = 83), middle-aged adults (40-64 years old; n = 52), and older adults (65-87 years old; n = 50) completed a questionnaire that assessed preference for temporal comparison or social comparison. Although the present results support the general assumption of the life-span model, they suggest that preferences for comparison processes develop in accordance with another pattern. Consistent with the life-span model, the present results indicate that temporary comparison is more important for young and middle-aged adults than researchers have assumed.

Adolescent↗

PubMed2001

A hybrid computational fluid dynamics and physiologically based pharmacokinetic model for comparison of predicted tissue concentrations of acrylic acid and other vapors in the rat and human nasal cavities following inhalation exposure.

To assist in interspecies dosimetry comparisons for risk assessment of the nasal effects of organic acids, a hybrid computational fluid dynamics (CFD) and physiologically based pharmacokinetic (PBPK) dosimetry model was constructed to estimate the regional tissue dose of inhaled vapors in the rat and human nasal cavity. Application to a specific vapor would involve the incorporation of the chemical-specific reactivity, metabolism, partition coefficients, and diffusivity (in both air and tissue phases) of the vapor. This report describes the structure of the CFD-PBPK model and its application to a representative acidic vapor, acrylic acid, for interspecies tissue concentration comparisons to assist in risk assessment. By using the results from a series of short-term in vivo studies combined with computer modeling, regional nasal tissue dose estimates were developed and comparisons of tissue doses between species were conducted. To make these comparisons, the assumption was made that the susceptibilities of human and rat olfactory epithelium to the cytotoxic effects of organic acids were similar, based on similar histological structure and common mode of action considerations. Interspecies differences in response were therefore assumed to be driven primarily by differences in nasal tissue concentrations that result from regional differences in nasal air flow patterns relative to the species-specific distribution of olfactory epithelium in the nasal cavity. The results of simulations with the seven-compartment CFD-PBPK model suggested that the olfactory epithelium of the human nasal cavity would be exposed to tissue concentrations of acrylic acid similar to that of the rat nasal cavity when the exposure conditions are the same. Similar analysis of CFD data and CFD-PBPK model simulations with a simpler one-compartment model of the whole nasal cavities of rats and humans provides comparable results to averaging over the compartments of the seven-compartment model. These results indicate that the general structure of the hybrid CFD-PBPK model applied in this assessment would be useful for target tissue dosimetry and interspecies dose comparisons for a wide variety of vapors. Because of its flexibility, this CFD-PBPK model is envisioned to be a platform for the construction of case-specific inhalation dosimetry models to simulate in vivo exposures that do not involve significant histopathological damage to the nasal cavity.

Acrylates↗

PubMed2001

Social comparison in Chinese older adults.

Depression is quite common among the elderly members of Hong Kong Chinese society. This study examined the role of social comparison in the relationship between depressive symptoms and four key life domains including: physical health, financial situation, relationships with adult children, and social support from friends. The respondents were 411 people aged 60 years or older from a survey of a representative community sample of the elderly population in Hong Kong. Using multiple regression models, the authors found that social comparison mediated the effect of support from friends on depressive symptoms and social comparison was the partial mediator in the linkage between financial strain and depressive symptoms. Moreover, social comparison also moderated the effect of physical health and support from friends on depressive symptoms. Lastly, we found that self-efficacy and self-esteem were moderators in the relationship between depressive symptoms and all four key life domains including physical health, financial situation, relationship with adult children, and social support from friends, whereas sense of control over physical health and sense of control over support from friends moderated the effect of social comparison on physical health and support from friends, respectively, on depressive symptoms.

Activities of Daily Living↗

PubMedDate not supplied

Ligand-receptor pairing via tree comparison.

This paper introduces a novel class of tree comparison problems strongly motivated by an important and cost intensive step in drug discovery pipeline viz., mapping cell bound receptors to the ligands they bind to and vice versa. Tree comparison studies motivated by problems such as virus-host tree comparison, gene-species tree comparison and consensus tree problem have been reported. None of these studies are applicable in our context because in all these problems, there is a well-defined mapping of the nodes the trees are built on across the set of trees being compared. A new class of tree comparison problems arises in cases where finding the correspondence among the nodes of the trees being compared is itself the problem. The problem arises while trying to find the interclass correspondence between the members of a pair of coevolving classes, e.g., cell bound receptors and their ligands. Given the evolution of the two classes, the combinatorial problem is to find a mapping among the leaves of the two trees that optimizes a given cost function. In this work we formulate various combinatorial optimization problems motivated by the aforementioned biological problem for the first time. We present hardness results, give an efficient algorithm for a restriction of the problem and demonstrate its applicability.

Algorithms↗