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PubMed1994

Noninvasive diagnosis of cardiac rejection through echocardiographic tissue characterization.

Ultrasonic tissue characterization is based on the assumption that microscopic tissue structures are identifiable by their acoustic properties. Our study group consisted of 23 cardiac recipients. Two-dimensional images were obtained within 2 hours of endomyocardial biopsy. The end-diastolic echo frames were digitized into the matrix of an image-processing system. A region of interest was placed into the anteroseptal segment of the left ventricle. The texture within the region of interest was analyzed using four major groups of texture analysis (first-order histogram, co-occurrence matrix, run-length statistic, and power spectrum). A total of 408 echocardiographic examinations were compared with histologic findings. The 117 initially calculated texture parameters were reduced incrementally using a series of discriminant analyses. A set of three texture parameters (inverse difference moment undirected, run-length nonuniformity vertical, and sector sum) was able to describe changed echocardiographic texture when rejection occurred. Using these three parameters, echocardiographic sensitivity was 89.0% and specificity was 83.6% for moderate rejection. We conclude that cardiac rejection is associated with echocardiographic texture alterations and that serial echocardiographic texture analysis can reliably identify rejection.

Adult↗
PubMed2000

Social motives and cognitive power-sex associations: predictors of aggressive sexual behavior.

The present study investigated whether implicit social motives and cognitive power-sex associations would predict self-reports of aggressive sexual behavior. Participants wrote stories in response to Thematic Apperception Test pictures, which were scored for power and affiliation-intimacy motives. They also completed a lexical-decision priming task that provided an index of the strength of the cognitive association between the concepts of "power" and "sexuality." For men, high levels of power motivation and strong power-sex associations predicted more frequent aggression. There was also an interaction: Power motivation was unrelated to aggression for men with the weakest power-sex associations. For women, high levels of affiliation-intimacy motivation were associated with more frequent aggression. Strong power-sex associations were also predictive for women but only when affiliation-intimacy motivation was high.

Adult↗
PubMed2006

Spectral mapping tools from the earth sciences applied to spectral microscopy data.

BACKGROUND: Spectral imaging, originating from the field of earth remote sensing, is a powerful tool that is being increasingly used in a wide variety of applications for material identification. Several workers have used techniques like linear spectral unmixing (LSU) to discriminate materials in images derived from spectral microscopy. However, many spectral analysis algorithms rely on assumptions that are often violated in microscopy applications. This study explores algorithms originally developed as improvements on early earth imaging techniques that can be easily translated for use with spectral microscopy. METHODS: To best demonstrate the application of earth remote sensing spectral analysis tools to spectral microscopy data, earth imaging software was used to analyze data acquired with a Leica confocal microscope with mechanical spectral scanning. For this study, spectral training signatures (often referred to as endmembers) were selected with the ENVI (ITT Visual Information Solutions, Boulder, CO) "spectral hourglass" processing flow, a series of tools that use the spectrally over-determined nature of hyperspectral data to find the most spectrally pure (or spectrally unique) pixels within the data set. This set of endmember signatures was then used in the full range of mapping algorithms available in ENVI to determine locations, and in some cases subpixel abundances of endmembers. RESULTS: Mapping and abundance images showed a broad agreement between the spectral analysis algorithms, supported through visual assessment of output classification images and through statistical analysis of the distribution of pixels within each endmember class. CONCLUSIONS: The powerful spectral analysis algorithms available in COTS software, the result of decades of research in earth imaging, are easily translated to new sources of spectral data. Although the scale between earth imagery and spectral microscopy is radically different, the problem is the same: mapping material locations and abundances based on unique spectral signatures.

Algorithms↗
PubMed1999

Validation of the empowerment scale with an outpatient mental health population.

The validity of the Empowerment Scale was examined in an adult outpatient mental health population. A survey was mailed to 2,000 consumers in the South Carolina outpatient public mental health system, and 283 completed surveys were received, a response rate of 16.5 percent. Reliability and factor analyses confirmed five subscales of empowerment: esteem, power, activism, anger, and control. Respondents with full-time jobs scored significantly higher on overall empowerment and on the esteem, anger, and power subscales. Respondents with college experience scored higher on overall empowerment and the power subscale. Results indicate adequate validity of the scale in this population and provide direction for research on empowerment as a process and outcome variable.

Adult↗
PubMed2005

A meta-analysis of controlled trials of recombinant human activated protein C therapy in patients with sepsis.

BACKGROUND: Meta-analysis of two randomised controlled trials in severe sepsis performed with recombinant human activated protein C may provide further insight as to the therapeutic utility of targeting the clotting cascade in this syndrome. METHODS: In search for relevant studies published, two randomized clinical trials were found eligible. RESULTS: The studies, PROWESS and ADDRESS, enrolled a total of 4329 patients with risk ratio (RR) and 95% confidence interval (CI) data for effect on 28-day mortality relative to control treatment of 0.92 (0.83-1.02) suggesting that recombinant human activated protein C is not beneficial in severe sepsis. In PROWESS, 873 of 1690 patients presented with low risk, and 2315 of 2639 patients in ADDRESS as defined by APACHE II score < 25. In this low-risk stratum, no effect of recombinant human activated protein C administration on 28-day mortality was observed. This observation appears to be consistent and homogenous. Heterogeneity between the two studies, however, was seen in patients with APACHE II score > or = 25 in whom recombinant activated protein C was effective in PROWESS (n = 817; RR 0.80, CI 0.68-0.94) whereas a tendency toward harm was present in ADDRESS (n = 324; RR 1.21, CI 0.85-1.74). Even though the overall treatment effect in this high-risk population was still in favour of treatment with recombinant activated protein C (n = 1141; RR 0.71, CI 0.59-0.85), the observed heterogeneity suggests that the efficacy of recombinant human activated protein C is not robust. Not unlikely, the adverse tendency observed could have become significant with higher statistical power would ADDRESS not have been terminated prematurely. CONCLUSION: This meta-analysis, therefore, raises doubts about the clinical usefulness of recombinant activated protein C in patients with severe sepsis and an APACHE II score > or = 25 which can only be resolved by another properly designed clinical trial.

Journal Article↗
PubMed1991

Statistical inference on mean dioptric power: asymmetric powers and singular covariance.

Methods have been developed recently for testing hypotheses on mean dioptric power and for constructing confidence regions in situations that are most likely to be encountered. In this paper the methods are extended to make the analysis complete. A new situation covered specifically is that of dioptric power not of the form sphere/cylinder x axis. Such powers, termed asymmetric powers because the dioptric power matrices are asymmetric, include the equivalent power of a thick obliquely crossed bitoric lens. A second situation is that in which the covariance matrix of the sample of powers is singular. Symmetric dioptric power (the more familiar form of power) can be represented by a point in three-dimensional space. In general, however, dioptric power is four dimensional in character. Singularity of covariance arises when variation in the sample is limited to a subspace of dimension less than the full three or four. The space spanned by the sample is called the range space of the sample. The dimension of the range space may be four, three, two, one or zero. Each case is considered in turn. Numerical examples of hypothesis testing are presented in range spaces of dimension four to one. The test statistic devised for each case also gives the equation of the confidence region about the mean of a sample of dioptric powers. Singularity can sometimes be avoided merely by taking larger samples and by taking more accurate readings. The problem of near singularity is briefly discussed. The paper allows basic hypothesis testing on mean dioptric power and the construction of confidence regions in all possible circumstances.

Multivariate Analysis↗
PubMed2001

Cerebrovascular reactivity in normal pregnancy and preeclampsia.

OBJECTIVE: To compare cerebrovascular reactivity in normotensive and preeclamptic pregnant women. METHODS: Transcranial Doppler ultrasound was used to measure peak, end-diastolic, and mean velocities in the middle cerebral arteries of 45 normotensive and 36 preeclamptic women in the third trimester. All measurements were done in the left lateral position at baseline, during 5% carbon dioxide (CO2) inhalation, and during an isometric hand-grip test. Blood pressure (BP), heart rate, oxygen (O2) saturation, and end-tidal partial pressure of carbon dioxide (pCO2) were recorded with each Doppler measurement. The mean pulsatility index (PI), resistance index (RI), and cerebral perfusion pressure at each time was compared using two-way repeated measures analysis of variance. Cerebrovascular reactivity, calculated as the percentage change in response to each maneuver, was also compared using analysis of covariance. A post hoc power analysis was performed to evaluate the primary measures of the study (middle cerebral artery PI and RI). Using alpha error of 5%, the statistical power to identify a difference in PI and RI in women with preeclampsia compared with normotensive women was 90% and 67%, respectively. The statistical power to identify a difference in PI and RI in response to the two maneuvers was 69% and 53%, respectively. Statistical significance was set at P <.05. RESULTS: Preeclamptic women had higher baseline cerebral perfusion pressure (90.4 compared with 61.9 mmHg, P <.05) and lower PI (0.64 compared with 0.76, P <.05) and RI (0.46 compared with 0.51, P <.05) than normotensive pregnant women. In normotensive patients, both 5% CO2 inhalation and isometric hand-grip test caused a significant decrease in PI (-9.5% and -6.1%, respectively) and RI (-6.5% and -4.2%, respectively). In contrast, in preeclamptic patients there was no change in any of the middle cerebral artery parameters in response to either maneuver. CONCLUSION: Normotensive pregnant women had normal middle cerebral artery responses to both 5% CO2 inhalation and isometric hand-grip test. Preeclamptic patients had elevated baseline cerebral perfusion pressure and reduced vasodilatory responses to both tests. These findings are consistent with a state of vasoconstriction in preeclamptic women that is unresponsive to stimuli that under normal circumstances result in vasodilation.

Adult↗
PubMed1999

Statistics of DNA sequences: a low-frequency analysis.

We study statistical properties of DNA chains of thirteen microbial complete genomes. We find that the power spectrum of several of the sequences studied flattens off in the low frequency limit. This implies the correlation length in those sequences is much smaller than the entire DNA chain. Consequently, in contradiction with previous studies, we show that the fractal behavior of DNA chains does not always prevail through the entire DNA molecule.

Biometry↗
PubMed2005

Multivariate analysis of paired watershed data to evaluate agricultural best management practice effects on stream water phosphorus.

Quantification of the effects of management programs on water quality is critical to agencies responsible for water resource protection. This research documents reductions in stream water phosphorus (P) loads resulting from agricultural best management practices (BMPs) implemented as part of an effort to control eutrophication of Cannonsville Reservoir, a drinking water supply for New York City. Dairy farms in the upstate New York reservoir basin were the target of BMPs designed to reduce P losses. A paired watershed study was established on one of these farms in 1993 to evaluate changes in P loading attributable to implementation of BMPs that included manure management, rotational grazing, and improved infrastructure. Intensive stream water monitoring provided data to calculate P loads from the 160-ha farm watershed for all runoff events during a two-year pre-treatment period and a four-year post-treatment period. Statistical control for inter-annual climatic variability was provided by matched P loads from a nearby 86-ha forested watershed, and by several event flow variables measured at the farm. A sophisticated multivariate analysis of covariance (ANCOVA) provided estimates of both seasonal and overall load reductions. Statistical power and the minimum detectable treatment effect (MDTE) were also calculated. The results demonstrated overall event load reductions of 43% for total dissolved phosphorus (TDP) and 29% for particulate phosphorus (PP). Changes in farm management practices and physical infrastructure clearly produced decreases in event P losses measurable at the small watershed scale.

Agriculture↗
PubMed2004

Assessment of angiogenesis: implications for ultrasound imaging.

In this paper, the fundamentals of tumor angiogenesis and the implications for ultrasound imaging will be described. Twenty-eight athymic nude mice were implanted with the human melanoma cell lines DB-1 or MW-9 (14 mice/group). Ultrasound contrast agents were injected in the tail veins. Power Doppler and pulse inversion harmonic imaging (PI-HI) was performed (in real time and intermittently). Ultrasound results were compared to immunohistochemical stains for endothelial cells (CD31), vascular endothelial growth factor (VEGF), and cyclooxygenase-2 (COX-2). Linear regression analysis indicated statistically significant correlations between percent area stained with COX-2 and with VEGF relative to power Doppler (p<0.05) and intermittent PI-HI (p<0.05) measures of tumor neovascularity in the MW-9 and the DB-1 mice, respectively. Preliminary results from a human trial of the anti-angiogenic drug Angiostatin (Entremed, Rockville, MD) showed tumor volumes increased in two patients, while the vascularity remained virtually unchanged. Conversely, in three patients with diminished tumor volumes vascularity increased by 38%. In conclusion, contrast enhanced ultrasound imaging of tumor neovascularity may provide noninvasive markers of angiogenesis and may become a useful tool for monitoring anti-angiogenic therapies in vivo.

Angiogenesis Inhibitors↗
PubMedDate not supplied

Crossover studies with continuous variables: power analysis.

The crossover design is a sensitive means of determining the efficacy of new drugs because it eliminates between-subject variability. However, if the response in the first period carries on into the second (carryover effect) or if time factors cannot be kept constant in a lengthy crossover (time effects), its statistical power may be jeopardized. This may be equally true if a negative correlation exists between treatment responses. We recently demonstrated that the crossover design with binary variables is a powerful method even if correlation between treatment responses is negative. Power analysis of crossover trials with continuous variables has not been explicitly studied. Using the Scheffé model for the assessment of treatment effect, carryover effect, and time effect, we drew power curves of hypothesized crossover studies with different levels of correlation between drug response. We demonstrate that the sensitivity of testing is largely dependent on the levels of correlation between drug response. When positive, we have a great deal of sensitivity with which to test treatment effect and little sensitivity to test carryover or time effect. When negative, the opposite is observed. The correlation level in a crossover comparison is a major determinant of the sensitivity of testing. Treatments from one class with one mode of action frequently have a positive correlation and should be particularly considered for crossover comparisons. With treatment comparisons of totally different classes of drugs/modes of action, the opposite is true. It is hoped that this work affects the design of future crossover trials.

Algorithms↗
PubMed1995

Fractal mechanisms and heart rate dynamics. Long-range correlations and their breakdown with disease.

Under healthy conditions, the normal cardiac (sinus) interbeat interval fluctuates in a complex manner. Quantitative analysis using techniques adapted from statistical physics reveals the presence of long-range power-law correlations extending over thousands of heartbeats. This scale-invariant (fractal) behavior suggests that the regulatory system generating these fluctuations is operating far from equilibrium. In contrast, it is found that for subjects at high risk of sudden death (e.g., congestive heart failure patients), these long-range correlations break down. Application of fractal scaling analysis and related techniques provides new approaches to assessing cardiac risk and forecasting sudden cardiac death, as well as motivating development of novel physiologic models of systems that appear to be heterodynamic rather than homeostatic.

Adult↗
PubMed2002

Statistical power of non-parametric tests: a quick guide for designing sampling strategies.

The importance of considering statistical power in marine pollution studies is unequivocal. However, the vast majority of ecological literature on power analysis focuses on parametric rather than non-parametric tests. This note describes a Monte Carlo simulation method for estimating the power of non-parametric tests. The method is illustrated using ordinal data.

Data Interpretation, Statistical↗
PubMed2000

Detection of macro-ecological patterns in South American hummingbirds is affected by spatial scale.

Scale is widely recognized as a fundamental conceptual problem in biology, but the question of whether species-richness patterns vary with scale is often ignored in macro-ecological analyses, despite the increasing application of such data in international conservation programmes. We tested for scaling effects in species-richness gradients with spatially scaled data for 241 species of South American hummingbirds (Trochilidae). Analyses revealed that scale matters above and beyond the effect of quadrat area. Species richness was positively correlated with latitude and topographical relief at ten different spatial scales spanning two orders of magnitude (ca. 12,300 to ca. 1,225,000 km2). Surprisingly, when the influence of topography was removed, the conditional variation in species richness explained by latitude fell precipitously to insignificance at coarser spatial scales. The perception of macro-ecological pattern thus depends directly upon the scale of analysis. Although our results suggest there is no single correct scale for macro-ecological analyses, the averaging effect of quadrat sampling at coarser geographical scales obscures the fine structure of species-richness gradients and localized richness peaks, decreasing the power of statistical tests to discriminate the causal agents of regional richness gradients. Ideally, the scale of analysis should be varied systematically to provide the optimal resolution of macro-ecological pattern.

Animals↗
PubMed1996

Pairwise analysis of radiation hybrid mapping data.

Two point lod scores are widely used in pedigree analysis as they provide a fast and efficient method of establishing linkage. Groups of markers that lie in close proximity to one another can be formed by admitting any locus that is linked to at least one existing member of the group with lod score greater than some predetermined value. It seems natural to extend this technique to Radiation Hybrid Mapping both for constructing groups of tightly linked loci that may then be analysed using more powerful statistics and as a method of ordering in its own right. A general extension of two point analysis is derived and the problems associated with radiation hybrid data are discussed. In particular, the additional parameters representing the probabilities of different fragments being retained (which have no parallel in classical linkage analysis) lead to a range of estimators of the breakage probability, O, which have equal and maximal likelihood. Ways of circumventing this problem are discussed along with the potential errors they introduce. Importantly the ambiguity in estimation of theta is not carried through to the lod score as this depends only on the maximum value of the likelihood and not on the particular value of theta at which it occurs. Thus even though two point analysis fails to provide robust estimates of either breakage probabilities or the distance between loci, it represents a simple and effective method of constructing linkage groups that may be analysed with more powerful statistical methods. This is particularly important given the large number of microsatellites, ESTs and candidate genes currently being typed on radiation hybrids.

Chromosome Mapping↗
PubMed2001

Thrombolytic therapy for acute ischemic stroke.

Available evidence of thrombolysis in acute ischemic stroke comes from a series of recent trials conducted in patients with acute stroke, and from a meta-analysis published in the Cochrane Library. The objective of this paper is to review the literature on tolerability and efficacy of thrombolytic therapy in patients with acute ischemic stroke, to find out what the level of evidence is for each thrombolytic drug, and what should consequently be done in the routine practice. This review is based on a bibliographic search of published meta-analyses of randomized trials, published randomized trials, and ongoing randomized trials, with the outcomes of disability, death, and symptomatic intracerebral hemorrhages (fatal or non-fatal). Our primary end-point is a combination of death and disability, in terms of "death or dependency", with dependency defined as a modified Rankin Score (mRS) of >/=3. The level of evidence for the efficacy of a thrombolytic treatment is considered sufficient if there is both a statistically significant effect in the meta-analysis of all randomized trials, without statistically significant heterogeneity, together with one adequately powered and designed conclusive trial. Streptokinase has a clearly harmful effect, without any demonstrated benefit and must not be used in patients with acute ischemic stroke. The level of evidence of an effect of intra-arterial pro-urokinase to reduce death or dependency is low, available data are sparse (only 220 patients), the estimation of its real efficacy and tolerability remains unclear, and its use in clinical practice is not presently justified. The efficacy of alteplase has been incompletely demonstrated because the results vary across trials and type of outcomes (death, death or dependency), and the cut-off of the disability scale. There is a significant heterogeneity in the effect on death or dependency. However, we can conclude that there is a beneficial effect, but its clinical application is limited because of the absence of adequate criteria to identify patients most likely to benefit from treatment. Overall the use of alteplase in patients with acute stroke was associated with some benefit, but it significantly increased total mortality in two trials. Given the observed confidence interval (CI), the results are compatible with, in the best situtation, 203 advoided death or dependency and 61 avoided death per 1000 treated patients, and at worst 77 avoided death or dependency and 38 extra deaths per 1000 treated patients. Further trials aimed at validating more discriminant selection criteria are mandatory.

Acute Disease↗
PubMed2003

Power and measures of effect size in analysis of variance with fixed versus random nested factors.

Ignoring a nested factor can influence the validity of statistical decisions about treatment effectiveness. Previous discussions have centered on consequences of ignoring nested factors versus treating them as random factors on Type I errors and measures of effect size (B. E. Wampold & R. C. Serlin). The authors (a) discuss circumstances under which the treatment of nested provider effects as fixed as opposed to random is appropriate; (b) present 2 formulas for the correct estimation of effect sizes when nested factors are fixed; (c) present the results of Monte Carlo simulations of the consequences of treating providers as fixed versus random on effect size estimates, Type I error rates, and power; and (d) discuss implications of mistaken considerations of provider effects for the study of differential treatment effects in psychotherapy research.

Analysis of Variance↗