WHAT WORKS BEST AND WHEN: ACCOUNTING FOR MULTIPLE SOURCES OF PURESELECTION BIAS IN PROGRAM EVALUATIONS

Most evaluations are still quasi‐experimental and most recent quasi‐experimental methodological research has focused on various types of propensity score matching to minimize conventional selection bias on observables. Although these methods create better‐matched treatment and comparison groups on observables, the issue of selection on unobservables still looms large. Thus, in the absence of being able to run randomized controlled trials (RCTs) or natural experiments, it is important to understand how well different regression‐based estimators perform in terms of minimizing pure selection bias, that is, selection on unobservables. We examine the relative magnitudes of three sources of pure selection bias: heterogeneous response bias, time‐invariant individual heterogeneity (fixed effects [FEs]), and intertemporal dependence (autoregressive process of order one [AR(1)]). Because the relative magnitude of each source of pure selection bias may vary in different policy contexts, it is important to understand how well different regression‐based estimators handle each source of selection bias. Expanding simulations that have their origins in the work of Heckman, LaLonde, and Smith ( 1999 ), we find that difference‐in‐differences (DID) using equidistant pre‐ and postperiods and FEs estimators are less biased and have smaller standard errors in estimating the Treatment on the Treated (TT) than other regression‐based estimators. Our data analysis using the Job Training Partnership Act (JTPA) program replicates our simulation findings in estimating the TT.     

Exploiting expressed sequence tag databases for the development and characterization of gene-derived simple sequence repeat markers in the opium poppy (Papaver somniferum L.) for forensic applications

Simple sequence repeat (SSR) markers in the opium poppy (Papaver somniferum L.) were identified from an expressed sequence tag (EST) database comprised of 20,340 sequences. In total, 2780 SSR-containing sequences were identified. The most frequent microsatellite had an AT/TA motif (37%). Twenty-two opium poppy EST-SSR markers were presently developed and polymorphisms of six markers (psom 2, 4, 12, 13, 17, and 22) were utilized in 135 individuals under narcotic control investigation. An average of three alleles per locus (range: 2-5 alleles) with a mean heterozygosity of 0.167 was detected. Six loci identified 29 unique profiles in 135 individuals. The EST-SSR markers exhibited small degrees of genetic differentiation (fixation index = 0.727, p < 0.001). Other variable markers will be needed to facilitate the forensic identification of the opium poppy for future cases. To determine the potential for cross-species amplification, six markers were tested in five Papaver genera species and two Eschscholzia genera. The psom 4 and psom 17 primer pair was transferable. This is the first study to report SSR markers of the opium poppy.     

J. Brunnée; S.J. Toope,Legitimacy and Legality in International Law: An Interactional Account,Cambridge University Press,Cambridge 2010, xviii + 411 pp., UK£60/US$105, ISBN 978-0-521-88065-7 (hardback); UK£29.99/ US$55, ISBN 978-0-521-70683-4 (paperback). doi: 10.1017/S0165070X11200056

Netherlands International Law Review -