On testing the significance of sets of genes

This paper discusses the problem of identifying differentially expressed groups of genes from a microarray experiment. The groups of genes are externally defined, for example, sets of gene pathways derived from biological databases. Our starting point is the interesting Gene Set Enrichment Analysis (GSEA) procedure of Subramanian et al. [Proc. Natl. Acad. Sci. USA 102 (2005) 15545--15550]. We study the problem in some generality and propose two potential improvements to GSEA: the maxmean statistic for summarizing gene-sets, and restandardization for more accurate inferences. We discuss a variety of examples and extensions, including the use of gene-set scores for class predictions. We also describe a new R language package GSA that implements our ideas.Comment: Published at http://dx.doi.org/10.1214/07-AOAS101 in the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

The Next Generation of Market-Based Environmental Policies

We examine what will be required if market-based environmental policy instruments are to become a major force in U.S. environmental policy. We define market-based instruments, and specify five categories: pollution charges; tradable permits; deposit refund systems; reducing market barriers; and eliminating government subsidies. We review major U.S. applications, including: EPA's emissions trading program; the leaded gasoline phasedown; water quality permit trading; CFC trading; SO2 allowance trading; and the RECLAIM program. We assess the U.S. experience in terms of the relatively limited use of these instruments and in terms of the mixed record of performance of implemented instruments. We ask how the next generation of market-based instruments can be advanced, focusing on four sets of approaches: improving program design; applying market-based instruments on the state level; implementing new Federal programs; and addressing long-term issues. We conclude with a brief prognosis of the likely future role of market-based instruments in U.S. environmental policy.

Beyond contested elections: the processes of bill creation and the fulfillment of democracy's promises

Long before 1996, earlier promises of 'development' had splintered into a million shards. Development -- defined as the use of state power to bring about social, political, and economic change in favor of the mass of the population almost everywhere had seemingly imploded. 5 Babies in the poorer countries could expect to live from ten to thirty years fewer than those born in industrialized countries. [TRUNCATED

Faint Light from Dark Matter: Classifying and Constraining Dark Matter-Photon Effective Operators

Even if Dark Matter (DM) is neutral under electromagnetism, it can still interact with the Standard Model (SM) via photon exchange from higher-dimensional operators. Here we classify the general effective operators coupling DM to photons, distinguishing between Dirac/Majorana fermion and complex/real scalar DM. We provide model-independent constraints on these operators from direct and indirect detection. We also constrain various DM-lepton operators, which induce DM-photon interactions via RG running or which typically arise in sensible UV-completions. This provides a simple way to quickly assess constraints on any DM model that interacts mainly via photon exchange or couples to SM leptons.Comment: 32 pages + appendices, 9 + 1 figures, 2 + 1 tables. v2: some clarifications and references added; conclusions unchanged; version published in JHE

Fluid Tasks and Fluid Teams: The Impact of Diversity in Experience and Team Familiarity on Team Performance

In this paper, we consider how the structures of tasks and teams interact to affect team performance. We study the effects of diversity in experience on a team's ability to respond to task changes, by separately examining interpersonal team diversity (i.e., differences in experience across the entire team) and intrapersonal team diversity (i.e., whether individuals on the team are more or less specialized). We also examine whether team familiarity - team members' prior experience working with one another - helps teams to better manage challenges created by task changes and greater interpersonal team diversity. Using detailed project- and individual-level data from an Indian software services firm, we find that the interaction of task-change with intrapersonal diversity is related to improved project performance, while the interaction of task-change with interpersonal diversity is related to diminished performance. Additionally, the interaction of team familiarity with interpersonal diversity is related to improved project performance in some cases. Our results highlight a need for more nuanced approaches to leveraging experience in team management.Diversity, Knowledge Work, Project Flexibility, Task Change, Team Familiarity

A Robust Estimation of the Effects of Taxation on Charitable Contributions

While many studies find that the tax-price elasticity of giving exceeds unity, several recent studies find the contrary. This is important because it can be shown that if the elasticity exceeds one, then allowing taxpayers to deduct charitable giving from their taxable income is efficient in the sense that the amount donated exceeds the loss to the treasury. Here we use Consumer Expenditure Survey data to estimate the price elasticity of all deductible contributions. Because specification tests reject the consistency of estimators such as Tobit or the two-stage Heckman we use the semiparametric method of Ahn and Powell (1993). Rather than selecting bandwidths through cross-validation we demonstrate that because high and low bandwidths lead to the standard linear model one may use visual inspection for bandwidth selection. We also do not use the covariance matrix estimator of Ahn and Powell, instead bootstrapping a confidence interval. These bootstraps are also used to remove the finite sample bias inherent in nonlinear estimators. In our results we find an elasticity estimate greater than unity for the Tobit and Heckman methods but less than one for the Ahn and Powell method. Because specification tests suggest that the likelihood assumptions ensuring the consistency of the Tobit and Heckman do not hold, our results suggest that previous high tax-price elasticities may be caused by misspecification. However, our estimate of the elasticity of contributions to just social welfare organizations exceeds unity. In this sense the deduction for those types of contributions is efficient.

Methods for design of hoppers. Silos, bins and bunkers for reliable gravity flow, for pharmaceutical, food, mineral and other applications

It is now four and a half decades since Andrew Jenike introduced the first integrated method for characterising powders for flow, and using this information to design a hopper that would discharge without hang-up. Sadly, many users and designers of hoppers still do not benefit from this, so a lot of process vessels in industry still suffer from rat-holing, arching and bridging. Objections of cost, time and questionable accuracy were levelled at the original hopper design method, in spite of the breakthrough it represented. However, over the last 40 years these problems have been overcome with the introduction of faster, easier to use and more sensitive powder flowability measurement techniques, and a lot of experience of what measurements matter with which materials and in what operational scenarios. This paper will pull together various lessons learned from many years of hopper and silo design projects, and show a practical approach to deciding (i) what flow pattern is required (mass flow or core flow), (ii) what measurements need to be made of the powder properties, and (iii) what design models should be used, based on the material being handled and the operational requirements of any given case

Discussion of "Least angle regression" by Efron et al

Discussion of ``Least angle regression'' by Efron et al. [math.ST/0406456

Variation in Experience and Team Familiarity: Addressing the Knowledge Acquisition-Application Problem

Prior work in organizational learning has failed to find a consistent effect of variation in experience on performance. While some studies find a positive relationship between these two variables, others find no effect or even a negative relationship. In this paper, we suggest that the differences in prior findings may be due to the failure to separate the processes of knowledge acquisition and knowledge application. While variation in experience may permit the acquisition of valuable knowledge, additional mechanisms may be necessary to enable the subsequent application of that knowledge in a team setting. We hypothesize that team familiarity - prior experience working with team members - may be such a mechanism. We use detailed project- and individual-level data from an Indian software services firm to examine the effects of team familiarity and variation in market experience on multiple measures of performance for over 1,100 software development projects Consistent with prior work, we find mixed results for the effect of variation in experience on performance. We do, however, see evidence of a moderating effect of team familiarity on the relationship between these two variables. Our paper identifies one mechanism for uniting knowledge acquisition and knowledge application and provides insight into how the management of experience accumulation affects the development of organizational capabilities.Experience, Knowledge, Software, Team Familiarity, Variation