Upward Bias (upward + bias)

Distribution by Scientific Domains


Selected Abstracts


Upward bias in odds ratio estimates from genome-wide association studies

GENETIC EPIDEMIOLOGY, Issue 4 2007
Chad Garner
Abstract Genome-wide association studies are carried out to identify unknown genes for a complex trait. Polymorphisms showing the most statistically significant associations are reported and followed up in subsequent confirmatory studies. In addition to the test of association, the statistical analysis provides point estimates of the relationship between the genotype and phenotype at each polymorphism, typically an odds ratio in case-control association studies. The statistical significance of the test and the estimator of the odds ratio are completely correlated. Selecting the most extreme statistics is equivalent to selecting the most extreme odds ratios. The value of the estimator, given the value of the statistical significance depends on the standard error of the estimator and the power of the study. This report shows that when power is low, estimates of the odds ratio from a genome-wide association study, or any large-scale association study, will be upwardly biased. Genome-wide association studies are often underpowered given the low , levels required to declare statistical significance and the small individual genetic effects known to characterize complex traits. Factors such as low allele frequency, inadequate sample size and weak genetic effects contribute to large standard errors in the odds ratio estimates, low power and upwardly biased odds ratios. Studies that have high power to detect an association with the true odds ratio will have little or no bias, regardless of the statistical significance threshold. The results have implications for the interpretation of genome-wide association analysis and the planning of subsequent confirmatory stages. Genet Epidemiol. 2007. 2007 Wiley-Liss, Inc. [source]


COMPARING STRENGTHS OF DIRECTIONAL SELECTION: HOW STRONG IS STRONG?

EVOLUTION, Issue 10 2004
Joe Hereford
Abstract The fundamental equation in evolutionary quantitative genetics, the Lande equation, describes the response to directional selection as a product of the additive genetic variance and the selection gradient of trait value on relative fitness. Comparisons of both genetic variances and selection gradients across traits or populations require standardization, as both are scale dependent. The Lande equation can be standardized in two ways. Standardizing by the variance of the selected trait yields the response in units of standard deviation as the product of the heritability and the variance-standardized selection gradient. This standardization conflates selection and variation because the phenotypic variance is a function of the genetic variance. Alternatively, one can standardize the Lande equation using the trait mean, yielding the proportional response to selection as the product of the squared coefficient of additive genetic variance and the mean-standardized selection gradient. Mean-standardized selection gradients are particularly useful for summarizing the strength of selection because the mean-standardized gradient for fitness itself is one, a convenient benchmark for strong selection. We review published estimates of directional selection in natural populations using mean-standardized selection gradients. Only 38 published studies provided all the necessary information for calculation of mean-standardized gradients. The median absolute value of multivariate mean-standardized gradients shows that selection is on average 54% as strong as selection on fitness. Correcting for the upward bias introduced by taking absolute values lowers the median to 31%, still very strong selection. Such large estimates clearly cannot be representative of selection on all traits. Some possible sources of overestimation of the strength of selection include confounding environmental and genotypic effects on fitness, the use of fitness components as proxies for fitness, and biases in publication or choice of traits to study. [source]


Is Financial Stress an Incentive for the Adoption of Businesslike Planning and Control in Local Government?

FINANCIAL ACCOUNTABILITY & MANAGEMENT, Issue 1 2000
A Comparative Study of Eight Dutch Municipalities
Hood has formulated the hypothesis that financial stress is a motive for the adoption of New Public Management (NPM), and particularly of businesslike instruments and styles in government. He has illustrated this hypothesis on a macro-level by comparing different OECD countries. The aim of this paper is to make a start with a micro-level test of this hypothesis by studying individual governmental organization, i.e. eight municipalities in the Netherlands. The financial stress hypothesis has been operationalised by assuming a negative relationship between the financial position of a municipality and the existence of businesslike planning and control instruments. The research shows that there is no evidence for the existence of this relationship. However, a conclusive judgement about the financial stress hypothesis seems to be impossible due to the fact that non-technical aspects of NPM were not taken into account, and also because of an , on average , upward bias in the financial position of the municipalities in the empirical investigation. [source]


The Euro Effect on Trade is not as Large as Commonly Thought,

OXFORD BULLETIN OF ECONOMICS & STATISTICS, Issue 4 2007
Maurice J. G. Bun
Abstract Existing studies on the impact of the euro on goods trade report increments between 5% and 40%. These estimates are based on standard panel gravity models for the level of trade. We show that the residuals from these models exhibit upward trends over time for the euro countries, and that this leads to an upward bias in the estimated euro effect. To correct for that, we extend the standard model by including a time trend that may have different effects across country-pairs. This results in an estimated euro impact of only 3%. [source]


Overconfident managers and external financing choice

REVIEW OF BEHAVIORAL FINANCE (ELECTRONIC), Issue 1 2010
Masaya Ishikawa
G30; G32 Abstract This study examines the relationship between managerial overconfidence and corporate financing decisions by constructing proxies for managerial overconfidence based on the track records of earnings forecasts in Japanese listed firms. We find that managers have the stable tendency to forecast overly upward earnings compared to actual ones and that their upward bias decreases the probability of issuing equity in the public market by about 4.7 percent per one standard error, which economically has the strongest impact on financing decisions. This tendency is observed when we employ alternative measures for managerial overconfidence and other model specifications. However, in private placements, the choice to offer equity is not always avoided by managers. This implies that managers place private equity with the expectation of the certification effect. Copyright 2010 John Wiley & Sons, Ltd. [source]


POST-CARTEL PRICING DURING LITIGATION

THE JOURNAL OF INDUSTRIAL ECONOMICS, Issue 4 2004
Joseph E. Harrington Jr.
Standard methods in the U.S. for calculating antitrust damages in price-fixing cases are shown to create a strategic incentive for firms to price above the non-collusive price after the cartel has been dissolved. This results in an overestimate of the but for price and an underestimate of the level of damages. The extent of this upward bias in the but for price is greater, the longer the cartel was in place and the more concentrated the industry. [source]


NEW ESTIMATES OF AUSTRALIAN PUBLIC BORROWING AND CAPITAL RAISED IN LONDON, 1849,1914

AUSTRALIAN ECONOMIC HISTORY REVIEW, Issue 2 2007
Article first published online: 7 JUN 200, Bernard Attard
Australia; capital market; debt; foreign exchange; statistics Current statistics of Australian public borrowing to 1914 suffer from several limits. On the basis of a comprehensive revision, an upward bias is shown in all the alternative time series of London borrowing, while statistics of local bond issues are derived for the first time. The new time series show the importance of the initial borrowing cycle during the 1850s and 1860s; the scale of debt repatriation from the mid-1890s; the interaction between domestic and overseas borrowing before the 1880s; and the potential significance of remittance as an ,invisible stabiliser' of the exchanges and alternative indirect source of capital imports. [source]