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Mean Effect (mean + effect)

Distribution by Scientific Domains
Medical Sciences50%

Terms modified by Mean Effect

  • mean effect size
    		•

    Selected Abstracts

    Community effects of praying mantids: a meta-analysis of the influences of species identity and experimental design

    ECOLOGICAL ENTOMOLOGY, Issue 4 2002
    William F. Fagan
    Abstract ,1. Generalist arthropod predators are ubiquitous in terrestrial ecosystems but experimental studies have yielded little agreement as to their effects on prey assemblages. Drawing on results from a suite of experimental field studies, a meta-analysis was conducted of the impact of praying mantids (Mantodea: Mantidae) on arthropod assemblages in order to identify predictable and unpredictable effects of these extremely generalised predators. 2. Results across different experiments were synthesised using the log response ratio framework, with a focus on quantifying net mantid impacts on arthropod density across taxonomic orders and trophic levels of arthropods, paying special attention to the contribution of mantid species identity and experimental design variables, such as the use of cages, length of experiment, and manipulated mantid density. 3. Calculated on a per mantid-day basis, the net impacts of Tenodera sinensis on arthropod density were generally weaker but more predictable than the effects of Mantis religiosa. Mantids in general had weak negative effects on density for most taxa but exhibited strong negative and positive effects on some taxa. Tenodera sinensis tended to have negative effects on Homoptera, Diptera, and Hemiptera and herbivores as a group, however M. religiosa exhibited greater variation in response of different taxa that appeared to be affected more strongly by experimental design. The effects of Stagmomantis carolina tended to be negative or non-significant. 4. Experimental cages had little influence on either the sign or magnitude of net community impacts for T. sinensis, however cage experiments reversed the sign of the mean effect for two of six taxonomic orders when the experimental predator was M. religiosa. Cages also increased the variability of effect size greatly for M. religiosa but not for T. sinensis. 5. It was concluded that it is possible to use log response ratios to determine general, predictable trends in a well-studied system. Similar meta-analyses of generalist predator effects in other systems should produce predictions of how these predators influence food webs, an important step towards defining more clearly the influences of generalist predators on community structure and dynamics. [source]

    Measurement non-invariance of DSM-IV narcissistic personality disorder criteria across age and sex in a population-based sample of Norwegian twins

    INTERNATIONAL JOURNAL OF METHODS IN PSYCHIATRIC RESEARCH, Issue 3 2010
    Thomas S. Kubarych
    Abstract We investigated measurement non-invariance of DSM-IV narcissistic personality disorder (NPD) criteria across age and sex in a population-based cohort sample of 2794 Norwegian twins. Age had a statistically significant effect on the factor mean for NPD. Sex had a statistically significant effect on the factor mean and variance. Controlling for these factor level effects, item-level analysis indicated that the criteria were functioning differently across age and sex. After correcting for measurement differences at the item level, the latent factor mean effect for age was no longer statistically significant. The mean difference for sex remained statistically significant after correcting for item threshold effects. The results indicate that DSM-IV NPD criteria perform differently in males and females and across age. Differences in diagnostic rates across groups may not be valid without correcting for measurement non-invariance. [source]

    The distribution of QTL additive and dominance effects in porcine F2 crosses

    JOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 3 2010
    J. Bennewitz
    Summary The present study used published quantitative trait loci (QTL) mapping data from three F2 crosses in pigs for 34 meat quality and carcass traits to derive the distribution of additive QTL effects as well as dominance coefficients. Dominance coefficients were calculated as the observed QTL dominance deviation divided by the absolute value of the observed QTL additive effect. The error variance of this ratio was approximated using the delta method. Mixtures of normal distributions (mixtures of normals) were fitted to the dominance coefficient using a modified EM-algorithm that considered the heterogeneous error variances of the data points. The results suggested clearly to fit one component which means that the dominance coefficients are normally distributed with an estimated mean (standard deviation) of 0.193 (0.312). For the additive effects mixtures of normals and a truncated exponential distribution were fitted. Two components were fitted by the mixtures of normals. The mixtures of normals did not predict enough QTL with small effects compared to the exponential distribution and to literature reports. The estimated rate parameter of the exponential distribution was 5.81 resulting in a mean effect of 0.172. [source]

    The Impact of Board Independence and CEO Duality on Firm Performance: A Quantile Regression Analysis for Indonesia, Malaysia, South Korea and Thailand

    BRITISH JOURNAL OF MANAGEMENT, Issue 3 2010
    Dendi Ramdani
    We study the effect of board independence and CEO duality on firm performance for a sample of stock-listed enterprises from Indonesia, Malaysia, South Korea and Thailand, applying quantile regression. Quantile regression is more powerful than classical linear regression since quantile regression can produce estimates for all conditional quantiles of the distribution of a response variable, whereas classical linear regression only estimates the conditional mean effects of a response variable. Moreover, quantile regression is better able to handle violations of the basic assumptions in classical linear regression. Our empirical evidence shows that the effect of board independence and CEO duality on firm performance is different across the conditional quantiles of the distribution of firm performance, something classical linear regression would leave unidentified. This finding suggests that estimating the quantile effect of a response variable can well be more insightful than estimating only the mean effect of the response variable. Additionally, we find a negative moderating effect of board size on the positive relationship between CEO duality and firm performance. [source]