Showing papers by "University of Iowa published in 2001"

Osteoporosis prevention, diagnosis, and therapy

Abstract: OBJECTIVES To clarify the factors associated with prevention, diagnosis, and treatment of osteoporosis, and to present the most recent information available in these areas. PARTICIPANTS From March 27-29, 2000, a nonfederal, nonadvocate, 13-member panel was convened, representing the fields of internal medicine, family and community medicine, endocrinology, epidemiology, orthopedic surgery, gerontology, rheumatology, obstetrics and gynecology, preventive medicine, and cell biology. Thirty-two experts from these fields presented data to the panel and an audience of 699. Primary sponsors were the National Institute of Arthritis and Musculoskeletal and Skin Diseases and the National Institutes of Health Office of Medical Applications of Research. EVIDENCE MEDLINE was searched for January 1995 through December 1999, and a bibliography of 2449 references provided to the panel. Experts prepared abstracts for presentations with relevant literature citations. Scientific evidence was given precedence over anecdotal experience. CONSENSUS PROCESS The panel, answering predefined questions, developed conclusions based on evidence presented in open forum and the literature. The panel composed a draft statement, which was read and circulated to the experts and the audience for public discussion. The panel resolved conflicts and released a revised statement at the end of the conference. The draft statement was posted on the Web on March 30, 2000, and updated with the panel's final revisions within a few weeks. CONCLUSIONS Though prevalent in white postmenopausal women, osteoporosis occurs in all populations and at all ages and has significant physical, psychosocial, and financial consequences. Risks for osteoporosis (reflected by low bone mineral density [BMD]) and for fracture overlap but are not identical. More attention should be paid to skeletal health in persons with conditions associated with secondary osteoporosis. Clinical risk factors have an important but poorly validated role in determining who should have BMD measurement, in assessing fracture risk, and in determining who should be treated. Adequate calcium and vitamin D intake is crucial to develop optimal peak bone mass and to preserve bone mass throughout life. Supplementation with these 2 nutrients may be necessary in persons not achieving recommended dietary intake. Gonadal steroids are important determinants of peak and lifetime bone mass in men, women, and children. Regular exercise, especially resistance and high-impact activities, contributes to development of high peak bone mass and may reduce risk of falls in older persons. Assessment of bone mass, identification of fracture risk, and determination of who should be treated are the optimal goals when evaluating patients for osteoporosis. Fracture prevention is the primary treatment goal for patients with osteoporosis. Several treatments have been shown to reduce the risk of osteoporotic fractures, including those that enhance bone mass and reduce the risk or consequences of falls. Adults with vertebral, rib, hip, or distal forearm fractures should be evaluated for osteoporosis and given appropriate therapy.

Empathy: Its ultimate and proximate bases.

Abstract: There is disagreement in the literature about the exact nature of the phenomenon of empathy. There are emotional, cogni- tive, and conditioning views, applying in varying degrees across species. An adequate description of the ultimate and proximate mecha- nism can integrate these views. Proximately, the perception of an object's state activates the subject's corresponding representations, which in turn activate somatic and autonomic responses. This mechanism supports basic behaviors (e.g., alarm, social facilitation, vicar- iousness of emotions, mother-infant responsiveness, and the modeling of competitors and predators) that are crucial for the reproduc- tive success of animals living in groups. The Perception-Action Model (PAM), together with an understanding of how representations change with experience, can explain the major empirical effects in the literature (similarity, familiarity, past experience, explicit teach- ing, and salience). It can also predict a variety of empathy disorders. The interaction between the PAM and prefrontal functioning can also explain different levels of empathy across species and age groups. This view can advance our evolutionary understanding of empa- thy beyond inclusive fitness and reciprocal altruism and can explain different levels of empathy across individuals, species, stages of de- velopment, and situations.

Relationship of core self-evaluations traits--self-esteem, generalized self-efficacy, locus of control, and emotional stability--with job satisfaction and job performance: a meta-analysis.

Abstract: Recently, Judge, Locke, and Durham (1997) proposed a higher order construct they termed core self-evaluations or, more simply, positive self-concept. According to Judge et al. (1997), this construct is a broad dispositional trait that is indicated by four more specific traits—self-esteem, generalized self-efficacy, locus of control, and emotional stability (low neuroticism). The core selfevaluations construct was originally proposed as a potential explanatory variable in the dispositional source of job satisfaction. Subsequently, Judge and colleagues also have argued that the construct should be related to work motivation and, ultimately, to job performance (Judge, Erez, & Bono, 1998). Investigations of a link between core self-evaluations and job performance, however, are lacking. Despite a lack of studies linking the core self-evaluations factor to job satisfaction and, especially, to job performance, three of the core traits (self-esteem, locus of control, and emotional stability) appear to be the most widely studied personality traits in personality and applied psychology.1 Yet, with the exception of emotional stability and job performance, we have found no metaanalyses of the relationship between any of these traits with either job satisfaction or job performance.2 Thus, the purpose of the present study is to provide a quantitative review of the literature that examines the relationship of the four core self-evaluation traits with job satisfaction and job performance. This study determines whether general relationships exist and, if so, what the magnitudes of these relationships are. In the next section, we provide a brief review of the four traits and discuss the possible relationship of these traits with both job satisfaction and job performance.

Satisfaction, Repurchase Intent, and Repurchase Behavior: Investigating the Moderating Effect of Customer Characteristics

Abstract: Despite the claim that satisfaction ratings are linked to repurchase behavior, few attempts can be found that relate satisfaction ratings to actual repurchase behavior. This article fills this void by presenting a conceptual model for relating satisfaction ratings and repurchase behavior. The model is based on the premise that ratings observed in a typical customer satisfaction survey are error-prone measures of the customer’s true satisfaction, and they may vary systematically on the basis of consumer characteristics. The authors apply the model to a large-scale study of 100,040 automotive customers. Results show that consumers with different characteristics have different thresholds such that, at the same level of rated satisfaction, repurchase rates are systematically different among different customer groups. The authors also find that the nature and extent of response bias in satisfaction ratings varies by customer characteristics. In one group, the response bias is so high that rated satisf...

Survey of Infections Due to Staphylococcus Species: Frequency of Occurrence and Antimicrobial Susceptibility of Isolates Collected in the United States, Canada, Latin America, Europe, and the Western Pacific Region for the SENTRY Antimicrobial Surveillance Program, 1997–1999

Abstract: Between January 1997 and December 1999, bloodstream isolates from 15,439 patients infected with Staphylococcus aureus and 6350 patients infected with coagulase-negative Staphylococcus species (CoNS) were referred by SENTRY-participating hospitals in the United States, Canada, Latin America, Europe, and the Western Pacific region. S. aureus was found to be the most prevalent cause of bloodstream infection, skin and soft-tissue infection, and pneumonia in almost all geographic areas. A notable increase in methicillin (oxacillin) resistance among community-onset and hospital-acquired S. aureus strains was observed in the US centers. The prevalence of methicillin (oxacillin)-resistant S. aureus varied greatly by region, site of infection, and whether the infection was nosocomial or community onset. Rates of methicillin resistance were extremely high among S. aureus isolates from centers in Hong Kong and Japan. Uniformly high levels of methicillin resistance were observed among CoNS isolates. Given the increasing multidrug resistance among staphylococci and the possible emergence of vancomycin-resistant strains, global strategies are needed to control emergence and spread of multiply resistant staphylococci.

A stabilized conforming nodal integration for Galerkin mesh-free methods

Abstract: Domain integration by Gauss quadrature in the Galerkin mesh-free methods adds considerable complexity to solution procedures. Direct nodal integration, on the other hand, leads to a numerical instability due to under integration and vanishing derivatives of shape functions at the nodes. A strain smoothing stabilization for nodal integration is proposed to eliminate spatial instability in nodal integration. For convergence, an integration constraint (IC) is introduced as a necessary condition for a linear exactness in the mesh-free Galerkin approximation. The gradient matrix of strain smoothing is shown to satisfy IC using a divergence theorem. No numerical control parameter is involved in the proposed strain smoothing stabilization. The numerical results show that the accuracy and convergent rates in the mesh-free method with a direct nodal integration are improved considerably by the proposed stabilized conforming nodal integration method. It is also demonstrated that the Gauss integration method fails to meet IC in mesh-free discretization. For this reason the proposed method provides even better accuracy than Gauss integration for Galerkin mesh-free method as presented in several numerical examples. Copyright © 2001 John Wiley & Sons, Ltd.

First multispacecraft ion measurements in and near the Earth's magnetosphere with the identical Cluster ion spectrometry (CIS) experiment

Abstract: . On board the four Cluster spacecraft, the Cluster Ion Spectrometry (CIS) experiment measures the full, three-dimensional ion distribution of the major magnetospheric ions (H+, He+, He++, and O+) from the thermal energies to about 40 keV/e. The experiment consists of two different instruments: a COmposition and DIstribution Function analyser (CIS1/CODIF), giving the mass per charge composition with medium (22.5°) angular resolution, and a Hot Ion Analyser (CIS2/HIA), which does not offer mass resolution but has a better angular resolution (5.6°) that is adequate for ion beam and solar wind measurements. Each analyser has two different sensitivities in order to increase the dynamic range. First tests of the instruments (commissioning activities) were achieved from early September 2000 to mid January 2001, and the operation phase began on 1 February 2001. In this paper, first results of the CIS instruments are presented showing the high level performances and capabilities of the instruments. Good examples of data were obtained in the central plasma sheet, magnetopause crossings, magnetosheath, solar wind and cusp measurements. Observations in the auroral regions could also be obtained with the Cluster spacecraft at radial distances of 4–6 Earth radii. These results show the tremendous interest of multispacecraft measurements with identical instruments and open a new area in magnetospheric and solar wind-magnetosphere interaction physics. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetopheric configuration and dynamics; solar wind - magnetosphere interactions)

A streaming ensemble algorithm (SEA) for large-scale classification

Abstract: Ensemble methods have recently garnered a great deal of attention in the machine learning community. Techniques such as Boosting and Bagging have proven to be highly effective but require repeated resampling of the training data, making them inappropriate in a data mining context. The methods presented in this paper take advantage of plentiful data, building separate classifiers on sequential chunks of training points. These classifiers are combined into a fixed-size ensemble using a heuristic replacement strategy. The result is a fast algorithm for large-scale or streaming data that classifies as well as a single decision tree built on all the data, requires approximately constant memory, and adjusts quickly to concept drift.

Gene expression in Pseudomonas aeruginosa biofilms

Abstract: Bacteria often adopt a sessile biofilm lifestyle that is resistant to antimicrobial treatment. Opportunistic pathogenic bacteria like Pseudomonas aeruginosa can develop persistent infections. To gain insights into the differences between free-living P. aeruginosa cells and those in biofilms, and into the mechanisms underlying the resistance of biofilms to antibiotics, we used DNA microarrays. Here we show that, despite the striking differences in lifestyles, only about 1% of genes showed differential expression in the two growth modes; about 0.5% of genes were activated and about 0.5% were repressed in biofilms. Some of the regulated genes are known to affect antibiotic sensitivity of free-living P. aeruginosa. Exposure of biofilms to high levels of the antibiotic tobramycin caused differential expression of 20 genes. We propose that this response is critical for the development of biofilm resistance to tobramycin. Our results show that gene expression in biofilm cells is similar to that in free-living cells but there are a small number of significant differences. Our identification of biofilm-regulated genes points to mechanisms of biofilm resistance to antibiotics.

A comparison of warfarin and aspirin for the prevention of recurrent ischemic stroke.

Abstract: Background Despite the use of antiplatelet agents, usually aspirin, in patients who have had an ischemic stroke, there is still a substantial rate of recurrence. Therefore, we investigated whether warfarin, which is effective and superior to aspirin in the prevention of cardiogenic embolism, would also prove superior in the prevention of recurrent ischemic stroke in patients with a prior noncardioembolic ischemic stroke. Methods In a multicenter, double-blind, randomized trial, we compared the effect of warfarin (at a dose adjusted to produce an international normalized ratio of 1.4 to 2.8) and that of aspirin (325 mg per day) on the combined primary end point of recurrent ischemic stroke or death from any cause within two years. Results The two randomized study groups were similar with respect to base-line risk factors. In the intention-to-treat analysis, no significant differences were found between the treatment groups in any of the outcomes measured. The primary end point of death or recurrent ischemi...

Some Practical Guidelines for Effective Sample Size Determination

Abstract: Sample size determination is often an important step in planning a statistical study—and it is usually a difficult one. Among the important hurdles to be surpassed, one must obtain an estimate of one or more error variances and specify an effect size of importance. There is the temptation to take some shortcuts. This article offers some suggestions for successful and meaningful sample size determination. Also discussed is the possibility that sample size may not be the main issue, that the real goal is to design a high-quality study. Finally, criticism is made of some ill-advised shortcuts relating to power and sample size.

Automatic lung segmentation for accurate quantitation of volumetric X-ray CT images

Abstract: Segmentation of pulmonary X-ray computed tomography (CT) images is a precursor to most pulmonary image analysis applications. This paper presents a fully automatic method for identifying the lungs in three-dimensional (3-D) pulmonary X-ray CT images. The method has three main steps. First, the lung region is extracted from the CT images by gray-level thresholding. Then, the left and right lungs are separated by identifying the anterior and posterior junctions by dynamic programming. Finally, a sequence of morphological operations is used to smooth the irregular boundary along the mediastinum in order to obtain results consistent with these obtained by manual analysis, in which only the most central pulmonary arteries are excluded from the lung region. The method has been tested by processing 3-D CT data sets from eight normal subjects, each imaged three times at biweekly intervals with lungs at 90% vital capacity. The authors present results by comparing their automatic method to manually traced borders from two image analysts. Averaged over all volumes, the root mean square difference between the computer and human analysis is 0.8 pixels (0.54 mm). The mean intrasubject change in tissue content over the three scans was 2.75%/spl plusmn/2.29% (mean/spl plusmn/standard deviation).

Across the Great Divide: Knowledge Creation and Transfer Between Practitioners and Academics

Abstract: Observers have long noted a considerable gap between organizational research findings and management practices. Although volumes have been written about the probable causes and consequences of this gap, surprisingly little empirical evidence exists concerning the various viewpoints. The articles in this forum provide data on the role of academic-practitioner relationships in both generating and disseminating knowledge across boundaries. The contributions of each article are summarized in light of recent theories of knowledge creation, and suggestions are made for increasing the value and relevance of future research to both academics and practitioners.

Carotid Intimal-Medial Thickness Is Related to Cardiovascular Risk Factors Measured From Childhood Through Middle Age The Muscatine Study

Abstract: Background Higher carotid intimal-medial thickness (IMT) is associated with cardiovascular risk factors and is predictive of coronary artery disease and stroke in older adults. Carotid IMT was measured in young and middle-aged adults to determine its relationship with risk factors measured (1) in childhood, (2) currently, and (3) as a “load” from childhood to adulthood. Methods and Results Carotid ultrasound studies were performed in 346 men and 379 women aged 33 to 42 years who were representative of a cohort followed since childhood and who live in Muscatine, Iowa. The mean of the measurements of maximal carotid IMT at 12 locations was determined for each subject. A medical questionnaire was completed, and measurements of anthropometric characteristics and risk factors were obtained. The mean maximum carotid IMT was 0.79±0.12 mm for men and 0.72±0.10 mm for women. On the basis of multivariable analysis, the significant current predictors of IMT were age and LDL cholesterol in both sexes and diastolic bl...

Idiopathic pulmonary fibrosis

Abstract: Idiopathic pulmonary fibrosis is a rapidly progressive illness of unknown cause characterized by sequential acute lung injury with subsequent scarring and end-stage lung disease. Treatment at present remains largely supportive, with evidence that patients' satisfaction and survival may be improved by referral to centers specializing in the evaluation of interstitial lung diseases. Although no drug therapy has clearly been demonstrated to benefit patients with idiopathic pulmonary fibrosis, a number of novel investigational agents hold promise for future study. Given the poor prognosis associated with idiopathic pulmonary fibrosis, patients should be referred to regional centers of expertise for enrollment in therapeutic clinical trials or for lung transplantation.

Identification of CpG oligonucleotide sequences with high induction of IFN‐α/β in plasmacytoid dendritic cells

Abstract: The immature plasmacytoid dendritic cell (PDC) is identical with the principal type I IFN-producing cell upon viral infection Oligodeoxynucleotides which contain unmethylated CpG motifs (CpG ODN) are recognized by the vertebrate immune system Previously, we described CpG ODN that strongly activate human B cells and human blood dendritic cells Here we describe distinct CpG-containing oligonucleotide sequences which, in contrast to previously described CpG ODN, induced high amounts of IFN-alpha and IFN-beta in peripheral blood mononuclear cells (PBMC) Intracellular staining for IFN-alpha revealed that within PBMC CpG ODN-induced IFN-alpha is produced exclusively by PDC Unlike IFN-alpha, TNF-alpha is up-regulated in PDC by all CpG ODN tested Purified PDC responded to CpG ODN, demonstrating direct activation of PDC by CpG ODN The most active sequence induced the production of up to 5 pg IFN-alpha per single PDC, resulting in more than 400 ng/ml IFN-alpha in the supernatant of PBMC enriched for PDC The potency of CpG ODN to stimulate IFN-alpha correlated with their ability to stimulate NK cell lytic activity, while purified NK cells did not respond to CpG ODN IFNgamma production in PBMC was dependent on CpG ODN-induced IFN-alpha/beta as demonstrated by IFN-alpha/beta blocking antibodies IFN-alpha-inducing CpG ODN strongly supported IFN-gamma production of TCR-triggered CD4 T cells but were less active than other CpG ODN in stimulating B cells In conclusion our results demonstrate that particular CpG ODN sequences exist which, due to high IFN-alpha/beta induction in PDC, induce a set of immune responses typical for viral infection

Reflections on the determinants of voluntary turnover

Abstract: Offers reflections on the study of the determinants of voluntary turnover based on empirical research conducted since 1972 at the University of Iowa (Iowa City) by Price, Mueller and their colleagues. The largest share of this research is constituted by 33 studies, mostly theses and dissertations. Reflections are offered about the causal model used and the measures advanced. Alternative models of voluntary turnover are described and possible future research is indicated. A measurement Appendix is also presented. The purpose of the paper is to improve the explanation of voluntary turnover.

The development of self-regulation in the first four years of life.

Abstract: This study examined longitudinally the development of self-regulation in 108 young children during the first 4 years of life. Children's committed compliance (when they eagerly embraced maternal agenda) and situational compliance (when they cooperated, but without a sincere commitment) were studied. Both forms of compliance were observed in "Do" contexts, in which the mothers requested that the children sustain unpleasant, tedious behavior, and in "Don't" contexts, in which they requested that the children suppress pleasant, attractive behavior. Children's internalization while alone in the similar contexts was also studied. Parallel assessments were conducted when the children were 14, 22, 33, and 45 months of age. At all ages, the Do context was much more challenging for children than the Don't context. Girls surpassed boys in committed compliance. Both forms of compliance were longitudinally stable, but only within a given context. Children's fearfulness and effortful control, observed and mother reported, correlated positively with committed compliance, but mostly in the Don't context. Committed, but not situational, compliance was linked to children's internalization of maternal rules, observed when the children were alone in the Do and Don't contexts. These links were both concurrent and longitudinal, context specific, and significant even after controlling for maternal power assertion. There was modest preliminary evidence that committed compliance may generalize to interactions with adults other than the mother.

Functional annotation of a full-length mouse cDNA collection

Abstract: The RIKEN Mouse Gene Encyclopaedia Project, a systematic approach to determining the full coding potential of the mouse genome, involves collection and sequencing of full-length complementary DNAs and physical mapping of the corresponding genes to the mouse genome. We organized an international functional annotation meeting (FANTOM) to annotate the first 21,076 cDNAs to be analysed in this project. Here we describe the first RIKEN clone collection, which is one of the largest described for any organism. Analysis of these cDNAs extends known gene families and identifies new ones.

Consistent image registration

Abstract: Presents a new method for image registration based on jointly estimating the forward and reverse transformations between two images while constraining these transforms to be inverses of one another. This approach produces a consistent set of transformations that have less pairwise registration error, i.e., better correspondence, than traditional methods that estimate the forward and reverse transformations independently. The transformations are estimated iteratively and are restricted to preserve topology by constraining them to obey the laws of continuum mechanics. The transformations are parameterized by a Fourier series to diagonalize the covariance structure imposed by the continuum mechanics constraints and to provide a computationally efficient numerical implementation. Results using a linear elastic material constraint are presented using both magnetic resonance and X-ray computed tomography image data. The results show that the joint estimation of a consistent set of forward and reverse transformations constrained by linear-elasticity give better registration results than using either constraint alone or none at all.

Comprehensive Approach to Verification and Validation of CFD Simulations—Part 1: Methodology and Procedures

Abstract: We present a comprehensive approach to verification and validation methodology and procedures for CFD simulations from an already developed CFD code applied without requiring availability of the source code for specified objectives, geometry, conditions, and available benchmark information. Concepts, definitions, and equations derived for simulation errors and uncertainties provide the overall mathematical framework. Verification is defined as a process for assessing simulation numerical uncertainty and, when conditions permit, estimating the sign and magnitude of the numerical error itself and the uncertainty in that error estimate. The approach for estimating errors and uncertainties includes (1) the option of treating the numerical error as deterministic or stochastic, (2) the use of generalized Richardson extrapolation for J input parameters, and (3) the concept of correction factors based on analytical benchmarks, which provides a quantitative metric to determine proximity of the solutions to the asymptotic range, accounts for the effects of higher-order terms, and are used for defining and estimating errors and uncertainties

Interaction with the NMDA receptor locks CaMKII in an active conformation

Abstract: Calcium- and calmodulin-dependent protein kinase II (CaMKII) and glutamate receptors are integrally involved in forms of synaptic plasticity that may underlie learning and memory. In the simplest model for long-term potentiation, CaMKII is activated by Ca2+ influx through NMDA (N-methyl-D-aspartate) receptors and then potentiates synaptic efficacy by inducing synaptic insertion and increased single-channel conductance of AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptors. Here we show that regulated CaMKII interaction with two sites on the NMDA receptor subunit NR2B provides a mechanism for the glutamate-induced translocation of the kinase to the synapse in hippocampal neurons. This interaction can lead to additional forms of potentiation by: facilitated CaMKII response to synaptic Ca2+; suppression of inhibitory autophosphorylation of CaMKII; and, most notably, direct generation of sustained Ca2+/calmodulin (CaM)-independent (autonomous) kinase activity by a mechanism that is independent of the phosphorylation state. Furthermore, the interaction leads to trapping of CaM that may reduce down-regulation of NMDA receptor activity. CaMKII-NR2B interaction may be prototypical for direct activation of a kinase by its targeting protein.

Homocysteine-induced endoplasmic reticulum stress causes dysregulation of the cholesterol and triglyceride biosynthetic pathways

Abstract: Hepatic steatosis is common in patients having severe hyperhomocysteinemia due to deficiency for cystathionine beta-synthase. However, the mechanism by which homocysteine promotes the development and progression of hepatic steatosis is unknown. We report here that homocysteine-induced endoplasmic reticulum (ER) stress activates both the unfolded protein response and the sterol regulatory element-binding proteins (SREBPs) in cultured human hepatocytes as well as vascular endothelial and aortic smooth muscle cells. Activation of the SREBPs is associated with increased expression of genes responsible for cholesterol/triglyceride biosynthesis and uptake and with intracellular accumulation of cholesterol. Homocysteine-induced gene expression was inhibited by overexpression of the ER chaperone, GRP78/BiP, thus demonstrating a direct role of ER stress in the activation of cholesterol/triglyceride biosynthesis. Consistent with these in vitro findings, cholesterol and triglycerides were significantly elevated in the livers, but not plasmas, of mice having diet-induced hyperhomocysteinemia. This effect was not due to impaired hepatic export of lipids because secretion of VLDL-triglyceride was increased in hyperhomocysteinemic mice. These findings suggest a mechanism by which homocysteine-induced ER stress causes dysregulation of the endogenous sterol response pathway, leading to increased hepatic biosynthesis and uptake of cholesterol and triglycerides. Furthermore, this mechanism likely explains the development and progression of hepatic steatosis and possibly atherosclerotic lesions observed in hyperhomocysteinemia.

Does Greater Firm-Specific Return Variation Mean More or Less Informed Stock Pricing?

Abstract: Roll (1988) observes low R2 statistics for common asset pricing models due to vigorousfirms-specific returns variation not associated with public information. He concludes (p. 56) that this implies â¬Seither private information or else occasional frenzy unrelated to concrete information.â¬?We show that firms and industries with lower market model R2 statistics exhibit higher association between current returns and future earnings, indicating more information about future earnings in current stock returns. This supports Rollâ¬"s first interpretation ⬠higher firms-specific returns variation as a fraction of total variation signals more information-laden stock prices and, therefore, more efficient stock markets.