Agnostic notes on regression adjustments to experimental data: Reexamining Freedman's critique

Freedman [Adv. in Appl. Math. 40 (2008) 180-193; Ann. Appl. Stat. 2 (2008) 176-196] critiqued ordinary least squares regression adjustment of estimated treatment effects in randomized experiments, using Neyman's model for randomization inference. Contrary to conventional wisdom, he argued that adjustment can lead to worsened asymptotic precision, invalid measures of precision, and small-sample bias. This paper shows that in sufficiently large samples, those problems are either minor or easily fixed. OLS adjustment cannot hurt asymptotic precision when a full set of treatment-covariate interactions is included. Asymptotically valid confidence intervals can be constructed with the Huber-White sandwich standard error estimator. Checks on the asymptotic approximations are illustrated with data from Angrist, Lang, and Oreopoulos's [Am. Econ. J.: Appl. Econ. 1:1 (2009) 136--163] evaluation of strategies to improve college students' achievement. The strongest reasons to support Freedman's preference for unadjusted estimates are transparency and the dangers of specification search.Comment: Published in at http://dx.doi.org/10.1214/12-AOAS583 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

An econometric analysis of the desktop computer hardware market

The purpose of this study was to compare six competing econometric models which depict the relationship between hardware characteristics and machine cost for the desktop computer market. The Box-Cox methodology and multiyear data were used to facilitate this comparison. The analysis validated that the Box-Cox methodology is a viable means for evaluating competing model formulations within the field of information systems research. The results were consistent with past research that suggested a double natural log model formulation for representing the functional relationships among variables when modeling machine cost as a function of hardware attributes. Further, the more complex power transformation model formulations suggested by the Box-Cox methodology did not significantly outperform the more traditional and simpler double natural log model. More specifically, the results indicated that variables related to primary memory and microchip tedinology have the largest impact on machine cost. Additionally, variables related to madiine connectivity, machine expandability, and year of observation were also found to be significant explanatory variables for machine cost

\u3cem\u3eRhizobium japonicum\u3c/em\u3e Mutants Defective in Symbiotic Nitrogen Fixation

Rhizobium japonicum strains 3I1b110 and 61A76 were mutagenized to obtain 25 independently derived mutants that produced soybean nodules defective in nitrogen fixation, as assayed by acetylene reduction. The proteins of both the bacterial and the plant portions of the nodules were analyzed by two-dimensional polyacrylamide gel electrophoresis. All of the mutants had lower-than-normal levels of the nitrogenase components, and all but four contained a prominent bacteroid protein not observed in wild-type bacteroids. Experiments with bacteria grown ex planta suggested that this protein was derepressed by the absence of ammonia. Nitrogenase component II of one mutant was altered in isoelectric point. The soluble plant fraction of the nodules of seven mutants had very low levels of heme, yet the nodules of five of these seven mutants contained the polypeptide of leghemoglobin. Thus, the synthesis of the globin may not be coupled to the content of available heme in soybean nodules. The nodules of the other two of these seven mutants lacked not only leghemoglobin but most of the other normal plant and bacteroid proteins. Ultrastructural examination of nodules formed by these two mutants indicated normal ramification of infection threads but suggested a problem in subsequent survival of the bacteria and their release from the infection threads

Sub-5 keV electron-beam lithography in hydrogen silsesquioxane resist

We fabricated 9–30 nm half-pitch nested Ls and 13–15 nm half-pitch dot arrays, using 2 keV electron-beam lithography with hydrogen silsesquioxane (HSQ) as the resist. All structures with 15 nm half-pitch and above were fully resolved. We observed that the 9 and 10-nm half-pitch nested Ls and the 13-nm-half-pitch dot array contained some resist residues. We obtained good agreement between experimental and Monte-Carlo-simulated point-spread functions at energies of 1.5, 2, and 3 keV. The long-range proximity effect was minimal, as indicated by simulated and patterned 30 nm holes in negative-tone resist.United States. Dept. of Energy. Office of Basic Energy Sciences (Award DE-SC0001088)National Science Foundation (U.S.) (Grant CMMI-0609241)China Scholarship CouncilNational Science Foundation (U.S.). Graduate Research Fellowshi

International E-Banking: ICT Investments and the Basel Accord

This study investigates how the Basel Accord and Information and Telecommunications Technologies (ICT) investments affect the commercial banking industries across countries. We employ the stochastic frontier approach to explore a data set composed of commercial banks from 51 countries. We find that telecommunications investment reduces, and the Basel Accord proxy enhances, the cost efficiency of commercial banks under study. Moreover, it is found that ICT investments improve cost efficiencies of commercial banks for countries in which the regulations are consistent with the international supervision

Efficiency Gains from the Relative Size of Information Technology Investments

The contribution of information technology (IT) to organizational performance has been investigated extensively in the MIS research recently. In this paper, the relationship between the relative size of IT investments by firms and the productive efficiency is examined using stochastic frontiers. We find evidence that the level of IT investments has a positive effect on the firm’s productive efficiency, implying that the firms investing relatively more in IT are likely to be more efficient in their production processes than those that invest less