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Smaller Sample (smaller + sample)

Distribution by Scientific Domains
Life Sciences22%
Chemistry22%

Terms modified by Smaller Sample

  • smaller sample size
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    Selected Abstracts

    Long-Term Performance Following Rights Issues and Open Offers in the UK

    JOURNAL OF BUSINESS FINANCE & ACCOUNTING, Issue 1-2 2007
    Proches Ngatuni
    Abstract:, This study finds evidence of significant long-term underperformance following rights issues made during 1986-95 in the UK. The findings are resilient to a number of methodological controls. In contrast, our results for a smaller sample of open offers made during 1991-95 show strong positive performance over a 5-year post-issue period, implying that firms making open offers had better growth prospects than firms making rights issues. During 1986-90, a period when open offers were rarely used, firms appeared to be making rights issues to exploit overvaluation. However, this was not evident for rights issues made during 1991-95, a period when open offers were more commonly used. [source]

    Sample size for post-marketing safety studies based on historical controls,

    PHARMACOEPIDEMIOLOGY AND DRUG SAFETY, Issue 8 2010
    Yu-te Wu
    Abstract Purpose As part of a drug's entire life cycle, post-marketing studies are an important part in the identification of rare, serious adverse events. Recently, the US Food and Drug Administration (FDA) has begun to implement new post-marketing safety mandates as a consequence of increased emphasis on safety. The purpose of this research is to provide exact sample size formula for the proposed hybrid design, based on a two-group cohort study with incorporation of historical external data. Methods Exact sample size formula based on the Poisson distribution is developed, because the detection of rare events is our outcome of interest. Performance of exact method is compared to its approximate large-sample theory counterpart. Results The proposed hybrid design requires a smaller sample size compared to the standard, two-group prospective study design. In addition, the exact method reduces the number of subjects required in the treatment group by up to 30% compared to the approximate method for the study scenarios examined. Conclusions The proposed hybrid design satisfies the advantages and rationale of the two-group design with smaller sample sizes generally required. Copyright © 2010 John Wiley & Sons, Ltd. [source]

    Nonadherence as a predictor of antidiabetic drug therapy intensification (augmentation),

    PHARMACOEPIDEMIOLOGY AND DRUG SAFETY, Issue 9 2004
    Dr Stephen J. Kogut MBA
    Abstract Purpose To determine if nonadherence with antidiabetic drug therapy is predictive of subsequent antidiabetic drug therapy intensification. Methods We conducted a retrospective cohort study examining retail pharmacy dispensings of sulfonylureas or metformin to 1067 patients having diabetes. Patients that did not receive a sufficient quantity of medication to cover at least 80% of days during the evaluation period were classified as nonadherent. Outcomes identified were increase in the dose of antidiabetic medication utilized, the addition of a second antidiabetic agent to the regimen or either. Results Among users of sulfonylurea monotherapy, those classified as nonadherent were 45% more likely to intensify therapy in subsequent months as compared with those classified as adherent (age-adjusted odds ratio (OR) 1.45; 95% confidence interval (CI) 1.06,2.00). This finding was largely driven by observed increases in dosage, which were more likely among patients classified as nonadherent (age-adjusted OR 1.48, 95%CI 1.07,2.05). Nonadherence was not found to be predictive of the subsequent addition of a second antidiabetic agent (OR 1.02; 95%CI 0.64,1.63). Overall findings were similar for the smaller sample of patients receiving metformin monotherapy, though observed differences did not achieve statistical significance. Conclusions Patients who were poorly adherent to oral antidiabetic drug therapy more frequently experienced an increase in the dose of medication prescribed, as compared to patients that were classified as adherent. This finding underscores the need for prescribers to consider nonadherence as a root cause when patients fail to achieve therapeutic goals. Copyright © 2004 John Wiley & Sons, Ltd. [source]

    Testosterone, physical activity, and somatic outcomes among Filipino males

    AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2010
    Lee T. Gettler
    Abstract Testosterone (T) facilitates male investment in reproduction in part through its anabolic effects on skeletal muscle. Traits like muscle and strength are energetically costly but are believed to enhance competitive ability in humans and other mammals. However, there are limited data on relationships between T and somatic outcomes in lean, non-western populations. We evaluate relationships between waking and pre-bed salivary T and adiposity, fat-free mass (FFM), arm muscle area (AMA), and grip strength (GS) in a large, population-based birth cohort of young adult Filipino males (20.8,22.6 years, n = 872). Data were collected as part of the Cebu Longitudinal Health and Nutrition Survey. Neither waking nor evening T predicted FFM, AMA, or GS. However, there were borderline or significant interactions between T and basketball playing (the most common team sport) and weight lifting as predictors of outcomes: higher waking T predicted higher FFM (activity × T interaction P < 0.01), AMA (interaction P < 0.1), and GS (interaction P < 0.02) among frequent basketball players, and GS (interaction P < 0.09) among the smaller sample of weight lifters. In contrast to clinical studies, but consistent with findings in several subsistence-level populations, T was positively related to adiposity in these lean young males, suggesting that energy status might regulate circulating T. Our findings support a role of the prewaking rise in T as a determinant of energetic allocation to lean mass and strength in the context of repeated muscular use and support the hypothesized role of T as a mediator of investment in costly somatic traits in human males. Am J Phys Anthropol 142:590,599, 2010. © 2010 Wiley-Liss, Inc. [source]

    Sugar Preferences in Nectar- and Fruit-Eating Birds: Behavioral Patterns and Physiological Causes,

    BIOTROPICA, Issue 1 2006
    Chris N. Lotz
    ABSTRACT Sucrose, glucose, and fructose are the three sugars that commonly occur in floral nectar and fruit pulp. The relative proportions of these three sugars in nectar and fruit in relation to the sugar preferences of pollinators and seed dispersers have received considerable attention. Based on the research of Herbert and Irene Baker and their collaborators, a dichotomy between sucrose-dominant hummingbird-pollinated flowers and hexose-dominant passerine flowers and fruits was proposed. Data on sugar preferences of several hummingbird species (which prefer sucrose) vs. a smaller sample of passerines (which prefer hexoses) neatly fitted this apparent dichotomy. This hummingbird,passerine dichotomy was strongly emphasized until the discovery of South African plants with sucrose-dominant nectars, which are pollinated by passerines that are able to digest, and prefer sucrose. Now we know that, with the exception of two clades, most passerines are able to assimilate sucrose. Most sugar preference studies have been conducted using a single, relatively high, sugar concentration in the nectar (ca 20%). Thus, we lack information about the role that sugar concentration might play in sugar selection. Because many digestive traits are strongly affected not only by sugar composition, but also by sugar concentration, we suggest that preferences for different sugar compositions are concentration-dependent. Indeed, recent studies on several unrelated nectar-feeding birds have found a distinct switch from hexose preference at low concentrations to sucrose preference at higher concentrations. Finally, we present some hypotheses about the role that birds could have played in molding the sugar composition of plant rewards. RESUMEN Sacarosa, glucosa y fructosa son los azúcares mas comunes en néctar floral y pulpa de fruta. La proporción relativa de estos azúcares en néctar floral y la pulpa de fruta han sido estudiadas en relación a las preferencias de azúcar de polinizadores y dispersores de semillas. Basandose en estudios de Herbert e Irene Baker y colaboradores se propuso la existencia de una dicotomía entre plantas con néctares ricos en sacarosa que son polinizadas por colibríes, y plantas con néctares y frutos ricos en hexosas que son polinizadas por paserinos. Datos sobre la preferencia de azúcares en varias especies de colibríes (que prefieren sacarosas) comparados con una pequeña muestra de paserinos (que prefieren hexosas) apoyan la existencia de la dicotomía propuesta. La dicotomía colibrí-paserino fue enfatizada por más de una década, hasta el descubrimiento de plantas sudafricanas con néctares ricos en sacarosa que son polinizadas por paserinos que prefieren sacarosa. Hoy sabemos que la mayoría de los paserinos, salvo los miembros de dos clados, pueden asimilar la sacarosa. La mayoría de los estudios sobre preferencias de azúcares han sido conducidos usando una sola concentración de azúcares en el néctar (ca 20%). Por lo tanto, carecemos de información sobre el papel que juega la concentración de azúcares en las preferencias de estos por las aves. Debido a que muchos procesos digestivos son afectados, no solo por la composición de azúcares, sino también por su concentración, sugerimos que las preferencias por diferentes azúcares dependerán de su concentración. Efectivamente, estudios recientes indican que diferentes aves prefieren alimentarse de hexosas a bajas concentraciones, y de sacarosa a altas concentraciones. Finalmente, presentamos algunas hipótesis sobre el papel que las aves pudieron haber tenido en la evolución de la composición de azúcares del néctar y la fruta que consumen. [source]

    On the design of ultrafast shutters for time-resolved synchrotron experiments

    JOURNAL OF SYNCHROTRON RADIATION, Issue 1 2007
    Milan Gembicky
    A comprehensive treatment of the limitations and possibilities for single-pulse selection in synchrotron operating modes with ,150,ns bunch separation, as occurs in the standard operating mode at the Advanced Photon Source, is presented. It is shown that the strength of available materials and allowable kinetic energy build-up limit single-bunch selection for this separation to sample sizes of ,100,µm, and that for minimization of kinetic energy build-up it is preferable to increase the r.p.m. within physically acceptable limits rather than increase the disc radius to obtain a desirable peripheral speed. A slight modification of the equal-bunch spacing standard fill patterns is proposed that allows use of samples as large as 500,µm. The corresponding peripheral speed of the chopper wheel is ,600,m,s,1, which is within the limits of high-strength titanium alloys. For smaller samples, peripheral speeds are proportionally lower. Versatility can be achieved with interchangeable chopper wheels and the use of different orientations of the rotation axis relative to the X-ray beam, which opens the possibility of larger, rather than one-of-a-kind, production runs. [source]

    Time-resolved synchrotron diffraction and theoretical studies of very short-lived photo-induced molecular species

    ACTA CRYSTALLOGRAPHICA SECTION A, Issue 2 2010
    Philip Coppens
    Definitive experimental results on the geometry of fleeting species are at the time of writing still limited to monochromatic data collection, but methods for modifications of the polychromatic Laue data to increase their accuracy and their suitability for pump,probe experiments have been implemented and are reviewed. In the monochromatic experiments summarized, excited-state conversion percentages are small when neat crystals are used, but are higher when photoactive species are embedded in an inert framework in supramolecular crystals. With polychromatic techniques and increasing source brightness, smaller samples down to tenths of a micrometre or less can be used, increasing homogeneity of exposure and the fractional population of the excited species. Experiments described include a series of transition metal complexes and a fully organic example involving excimer formation. In the final section, experimental findings are compared with those from theoretical calculations on the isolated species. Qualitative agreement is generally obtained, but the theoretical results are strongly dependent on the details of the calculation, indicating the need for further systematic analysis. [source]

    Nonparametric covariate adjustment for receiver operating characteristic curves

    THE CANADIAN JOURNAL OF STATISTICS, Issue 1 2010
    Fang Yao
    Abstract The accuracy of a diagnostic test is typically characterized using the receiver operating characteristic (ROC) curve. Summarizing indexes such as the area under the ROC curve (AUC) are used to compare different tests as well as to measure the difference between two populations. Often additional information is available on some of the covariates which are known to influence the accuracy of such measures. The authors propose nonparametric methods for covariate adjustment of the AUC. Models with normal errors and possibly non-normal errors are discussed and analyzed separately. Nonparametric regression is used for estimating mean and variance functions in both scenarios. In the model that relaxes the assumption of normality, the authors propose a covariate-adjusted Mann,Whitney estimator for AUC estimation which effectively uses available data to construct working samples at any covariate value of interest and is computationally efficient for implementation. This provides a generalization of the Mann,Whitney approach for comparing two populations by taking covariate effects into account. The authors derive asymptotic properties for the AUC estimators in both settings, including asymptotic normality, optimal strong uniform convergence rates and mean squared error (MSE) consistency. The MSE of the AUC estimators was also assessed in smaller samples by simulation. Data from an agricultural study were used to illustrate the methods of analysis. The Canadian Journal of Statistics 38:27,46; 2010 © 2009 Statistical Society of Canada La précision d'un test diagnostique est habituellement établie en utilisant les courbes caracté-ristiques de fonctionnement du récepteur (« ROC »). Des statistiques telles que l'aire sous la courbe ROC (« AUC ») sont utilisées afin de comparer différents tests et pour mesurer la différence entre deux populations. Souvent de l'information supplémentaire est disponible sur quelques covariables dont l'influence sur de telles statistiques est connue. Les auteurs suggèrent des méthodes non paramétriques afin d'ajuster la statistique AUC pour prendre en compte les covariables. Des modèles avec des erreurs gaussiennes et même non gaussiennes sont présentés et analysés séparément. Une régression non paramétrique est utilisée afin d'estimer les fonctions moyenne et variance dans les deux scénarios. Pour le modèle sans l'hypothèse de normalité, les auteurs proposent un estimateur de Mann-Whithney tenant compte des covariables pour l'AUC qui utilise l'information disponible dans les données afin de construire des échantillons d'analyse pour n'importe quelle valeur des covariables. Cet estimateur est implanté, car il est calculable de façon efficace. Il généralise l'approche de Mann-Whitney pour comparer deux populations en considérant l'effet des covariables. Les auteurs obtiennent les propriétés asymptotiques des estimateurs AUC pour les deux scénarios incluant la normalité asymptotique, les vitesses optimales de convergence uniforme forte et la convergence en erreur quadratique moyenne (« MSE »). Le MSE de l'estimateur de l'AUC est aussi étudié pour les petits échantillons à l'aide de simulations. Des données provenant d'une étude dans le domaine agricole sont utilisées afin d'illustrer les méthodes d'analyse. La revue canadienne de statistique 38: 27,46; 2010 © 2009 Sociètè statistique du Canada [source]

    Luminescence dating: where it has been and where it is going

    BOREAS, Issue 4 2008
    ANN G. WINTLE
    The luminescence properties of common minerals, such as quartz and potassium-rich feldspars, allow them to be used to measure depositional ages for late Quaternary sediments. The optically stimulated luminescence (OSL) signals currently used are appropriate for mineral grains whose previous radiation history was erased by exposure to sunlight immediately prior to deposition. However, the concepts relating to grain size and long-term stability of the signals established when using the thermoluminescence signals should not be forgotten. Recent technological advances and the development of new laboratory measurement procedures for obtaining the equivalent dose have resulted in more widespread and more confident use of OSL for dating using smaller samples, even down to the single grain level. Ages can now be obtained for samples only a few hundred years old, and new luminescence signals are being investigated in order to extend the age range back by an order of magnitude from ,100 kyr to ,1 Myr. [source]