An equivalence result for VC classes of sets

Let R and θ be infinite sets and let A # R × θ. We show that the class of projections of A onto R is a Vapnik–Chervonenkis (VC) class of sets if and only if the class of projections of A onto θ is a VC class. We illustrate the result in the context of semiparametric estimation of a transformation model. In this application, the VC property is hard to establish for the projection class of interest but easy to establish for the other projection class

CHOICE OF REGRESSION METHOD FOR DETRENDING TIME SERIES DATA WITH NONNORMAL ERRORS

Research Methods/ Statistical Methods,

WEEDSIM: A BIOECONOMIC MODEL OF WEED MANAGEMENT IN CORN

Crop Production/Industries,

Anolis bahorucoensis

Number of Pages: 3Integrative BiologyGeological Science

Visual, Motor and Attentional Influences on Proprioceptive Contributions to Perception of Hand Path Rectilinearity during Reaching

We examined how proprioceptive contributions to perception of hand path straightness are influenced by visual, motor and attentional sources of performance variability during horizontal planar reaching. Subjects held the handle of a robot that constrained goal-directed movements of the hand to the paths of controlled curvature. Subjects attempted to detect the presence of hand path curvature during both active (subject driven) and passive (robot driven) movements that either required active muscle force production or not. Subjects were less able to discriminate curved from straight paths when actively reaching for a target versus when the robot moved their hand through the same curved paths. This effect was especially evident during robot-driven movements requiring concurrent activation of lengthening but not shortening muscles. Subjects were less likely to report curvature and were more variable in reporting when movements appeared straight in a novel “visual channel” condition previously shown to block adaptive updating of motor commands in response to deviations from a straight-line hand path. Similarly, compromised performance was obtained when subjects simultaneously performed a distracting secondary task (key pressing with the contralateral hand). The effects compounded when these last two treatments were combined. It is concluded that environmental, intrinsic and attentional factors all impact the ability to detect deviations from a rectilinear hand path during goal-directed movement by decreasing proprioceptive contributions to limb state estimation. In contrast, response variability increased only in experimental conditions thought to impose additional attentional demands on the observer. Implications of these results for perception and other sensorimotor behaviors are discussed

Factor Returns, Institutions, and Geography: A View From Trade

We examine the importance of institutions and geography for determining workers' wages and the return to capital. These returns to labor and capital are examined through the lens of labor and capital's productivities, which are directly related to the factors' returns. We estimate productivities of labor and capital based on trade flows across countries and present statistical evidence that these productivities are related to total factor productivities which rationalize output differences across countries. We examine whether these labor and capital productivities are related to countries' political institutions and geography. Protection of property rights is the dominant influence on both labor and capital productivity. There is some evidence that a democratic government affects productivity, but once property rights are included in the analysis, the overall democracy index has little influence on factor productivity.. Geography is only important in terms of distance to a large market. Factors such as the incidence of malaria are relatively unimportant. The unimportance of geography is not only statistical. For example, if the Philippines kept its geography but had the United Kingdom 's institutions, the Philippines ' labor productivity would increase from seven percent to 75 percent of the U.S. 's and capital productivity would increase from 25 percent to 58 percent of the U.S. 's. On the other hand, if the Philippines were to keep its institutions and were magically more to the United Kingdom 's geographic location, labor productivity would increase only from seven percent to 28 percent and capital productivity would increase from 25 percent to 26 percent.

How important are capital and total factor productivity for economic growth?

The authors examine the relative importance of the growth of physical and human capital and the growth of total factor productivity (TFP) using newly organized data on 145 countries that span more than one hundred years for twenty-four of these countries. For all countries, only 3 percent of average output growth per worker is associated with TFP growth. This world average masks interesting variations across countries and regions. Of the nine regions, TFP growth accounts for about twenty percent of average output growth in three regions and between ten and zero percent in the other three regions. In three regions, TFP growth is negative on average. The authors use priors from theories to construct estimates of the relative importance of the variances of aggregate input growth and TFP growth for the variance of output growth across countries. Across all countries, variation in aggregate input growth per worker could account for as much as 35 percent of the variance of the growth of output per worker across countries, and variation in TFP growth could account for as much as 87 percent of that variance. Much of the importance of the variance of TFP growth appears to be associated with negative TFP growth.Productivity ; Economic development ; Capital ; Industrial productivity

A Speculative Bubble in Commodity Futures Prices? Cross-Sectional Evidence

Recent accusations against speculators in general and long-only commodity index funds in particular, include: increasing market volatility, distorting historical price relationships, and fueling a rapid increase and decrease in commodity inflation. Some researchers have argued that these market participants—through their impact on market prices—may inadvertently prevented the efficient distribution of food aid to deserving groups. Certainly, this result—if substantiated— would counter the classical argument that speculators make prices more efficient and thus improve the economic efficiency of the agricultural and food marketing system. Given the very important policy implications, it is crucial to develop a more thorough understanding of long-only index funds and their potential market impact. Here, we review the criticisms (and rebuttals) levied against (and for) commodity index funds in recent U.S. Congressional testimonies. Then, additional empirical evidence is added regarding cross-sectional market returns and the relative levels of long-only index fund participation in 12 commodity futures markets. The results suggest that index fund positions across futures markets have no impact on relative price changes across those markets. The empirical results provide no evidence that long-only index funds impact commodity futures prices.Commitment’s of Traders, index funds, commodity futures markets, Agribusiness, Agricultural Finance, Farm Management, Financial Economics, Research Methods/ Statistical Methods, Risk and Uncertainty,

The Adequacy of Speculation in Agricultural Futures Markets: Too Much of a Good Thing?

The objective of this report is to re-visit the “adequacy of speculation” debate in agricultural futures markets. The Commodity Futures Trading Commission makes available the positions held by index funds and other large traders in their Commitment of Traders reports. The results suggest that after an initial surge from early 2004 through mid-2005, index fund positions have stabilized as a percent of total open interest. Traditional speculative measures do not show any material changes or shifts over the sample period. In most markets, the increase in long speculative positions was equaled or surpassed by an increase in short hedging. So, even after adjusting speculative indices for index fund positions, values are within the historical ranges reported in prior research. One implication is that long-only index funds may be beneficial in markets traditionally dominated by short hedging. Attempts to curb speculation through regulatory means should be weighed carefully against the potential benefits provided by this class of speculators.Commitment’s of Traders, index funds, commodity futures markets, Agricultural Finance, Financial Economics,