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Equal Magnitude (equal + magnitude)

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Business, Economics, Finance and Accounting60%

Selected Abstracts

Census error and the detection of density dependence

JOURNAL OF ANIMAL ECOLOGY, Issue 4 2006
ROBERT P. FRECKLETON
Summary 1Studies aiming to identify the prevalence and nature of density dependence in ecological populations have often used statistical analysis of ecological time-series of population counts. Such time-series are also being used increasingly to parameterize models that may be used in population management. 2If time-series contain measurement errors, tests that rely on detecting a negative relationship between log population change and population size are biased and prone to spuriously detecting density dependence (Type I error). This is because the measurement error in density for a given year appears in the corresponding change in population density, with equal magnitude but opposite sign. 3This effect introduces bias that may invalidate comparisons of ecological data with density-independent time-series. Unless census error can be accounted for, time-series may appear to show strongly density-dependent dynamics, even though the density-dependent signal may in reality be weak or absent. 4We distinguish two forms of census error, both of which have serious consequences for detecting density dependence. 5First, estimates of population density are based rarely on exact counts, but on samples. Hence there exists sampling error, with the level of error depending on the method employed and the number of replicates on which the population estimate is based. 6Secondly, the group of organisms measured is often not a truly self-contained population, but part of a wider ecological population, defined in terms of location or behaviour. Consequently, the subpopulation studied may effectively be a sample of the population and spurious density dependence may be detected in the dynamics of a single subpopulation. In this case, density dependence is detected erroneously, even if numbers within the subpopulation are censused without sampling error. 7In order to illustrate how process variation and measurement error may be distinguished we review data sets (counts of numbers of birds by single observers) for which both census error and long-term variance in population density can be estimated. 8Tests for density dependence need to obviate the problem that measured population sizes are typically estimates rather than exact counts. It is possible that in some cases it may be possible to test for density dependence in the presence of unknown levels of census error, for example by uncovering nonlinearities in the density response. However, it seems likely that these may lack power compared with analyses that are able to explicitly include census error and we review some recently developed methods. [source]

The asymmetric effects of uncertainty on inflation and output growth

JOURNAL OF APPLIED ECONOMETRICS, Issue 5 2004
Kevin B. Grier
We study the effects of growth volatility and inflation volatility on average rates of output growth and inflation for post-war US data. Our results suggest that increased growth uncertainty is associated with significantly lower average growth, while higher inflation uncertainty is significantly negatively correlated with lower output growth and lower average inflation. Both inflation and growth display evidence of significant asymmetric response to positive and negative shocks of equal magnitude. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Stability of choices in a risky decision-making task: a 3-year longitudinal study with children and adults

JOURNAL OF BEHAVIORAL DECISION MAKING, Issue 3 2007
Irwin P. Levin
Abstract In a 3-year follow-up to Levin and Hart's (2003) study, we observed the same children, now 9,11 years old, and their parents in the same risky decision-making task. At the aggregate level the same pattern of means was observed across time periods. At the individual level the key variables were significantly correlated across time periods for both children and adults. Taken together with the results from the original study and earlier studies, these results solidify the following conclusions: children utilize both probability and outcome information in risky decision-making; the tendency to make more risky choices to avoid a loss than to achieve a gain of equal magnitude, which is a major tenet of the leading theories of risky decision-making, occurs for children as well as adults; children make more risky choices than adults; temperamental predictors of risky choice are valid for children as well as for adults. Copyright © 2006 John Wiley & Sons, Ltd. [source]

A novel internal antenna with high gain for wireless phone

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 9 2007
Ying Liu
Abstract A novel internal antenna for synchronous code division multiple access band wireless phone is presented. Traditional internal antenna is monopole or Planar Inverted-F Antenna, which have no gain high enough in the limited space in phone. The proposed antenna is composed of two antenna elements with equal magnitude and 180° phase difference, to assure voice quality with high gain. The measured maximum gain is 2.69 dBi and maximum efficiency is 70.1% in the frequency band 450,470 MHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2112,2114, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22708 [source]

Australian Economic Growth: Nonlinearities and International Influences

THE ECONOMIC RECORD, Issue 235 2000
ÓLAN T. HENRY
This paper considers the extent to which fluctuations in Australian economic growth are affected by domestic and overseas economic performance. We investigate the performance of a range of nonlinear models versus linear models, comparing the models using Bayes factors and posterior odds ratios. The posterior odds ratios favour nonlinear specifications in which fluctuations in economic activity in the US affect Australia's economic performance. Our results suggest that an exogenous negative shock will be more persistent, lead to greater output volatility, and have a greater impact on growth, than a positive shock of equal magnitude. [source]