A Zero-Inflated Box-Cox Normal Unipolar Item Response Model for Measuring Constructs of Psychopathology

This research introduces a latent class item response theory (IRT) approach for modeling item response data from zero-inflated, positively skewed, and arguably unipolar constructs of psychopathology. As motivating data, the authors use 4,925 responses to the Patient Health Questionnaire (PHQ-9), a nine Likert-type item depression screener that inquires about a variety of depressive symptoms. First, Lucke’s log-logistic unipolar item response model is extended to accommodate polytomous responses. Then, a nontrivial proportion of individuals who do not endorse any of the symptoms are accounted for by including a nonpathological class that represents those who may be absent on or at some floor level of the latent variable that is being measured by the PHQ-9. To enhance flexibility, a Box-Cox normal distribution is used to empirically determine a transformation parameter that can help characterize the degree of skewness in the latent variable density. A model comparison approach is used to test the necessity of the features of the proposed model. Results suggest that (a) the Box-Cox normal transformation provides empirical support for using a log-normal population density, and (b) model fit substantially improves when a nonpathological latent class is included. The parameter estimates from the latent class IRT model are used to interpret the psychometric properties of the PHQ-9, and a method of computing IRT scale scores that reflect unipolar constructs is described, focusing on how these scores may be used in clinical contexts

Synaptic shot noise and conductance fluctuations affect the membrane voltage with equal significance

The subthresholdmembranevoltage of a neuron in active cortical tissue is a fluctuating quantity with a distribution that reflects the firing statistics of the presynaptic population. It was recently found that conductancebased synaptic drive can lead to distributions with a significant skew. Here it is demonstrated that the underlying shot noise caused by Poissonian spike arrival also skews the membrane distribution, but in the opposite sense. Using a perturbative method, we analyze the effects of shot noise on the distribution of synaptic conductances and calculate the consequent voltage distribution. To first order in the perturbation theory, the voltage distribution is a gaussian modulated by a prefactor that captures the skew. The gaussian component is identical to distributions derived using current-based models with an effective membrane time constant. The well-known effective-time-constant approximation can therefore be identified as the leading-order solution to the full conductance-based model. The higher-order modulatory prefactor containing the skew comprises terms due to both shot noise and conductance fluctuations. The diffusion approximation misses these shot-noise effects implying that analytical approaches such as the Fokker-Planck equation or simulation with filtered white noise cannot be used to improve on the gaussian approximation. It is further demonstrated that quantities used for fitting theory to experiment, such as the voltage mean and variance, are robust against these non-Gaussian effects. The effective-time-constant approximation is therefore relevant to experiment and provides a simple analytic base on which other pertinent biological details may be added

Immigrant Legalization: Assessing the Labor Market Effects

Assesses the effects of a legalization program for unauthorized immigrants on the labor market, tax revenues, and public assistance programs. Estimates immigrants' economic mobility by visa status and skill level as well as eligibility for benefits

U.S. and Swedish Direct Investment and Exports

Overseas production in a country by affiliates of Swedish and U.S. firms rarely appears to displace exports from the two home countries and in most cases either has no effect or tends to increase home country exports. The positive effect on Swedish exports is evident not only with respect to levels of exports to different countries at one time but also with respect to changes in exports over time. The positive effect on U.S. exports can be observed for minority-owned as well as majority-owned foreign operations.

Did Employer Sanctions Lose Their Bite? Labor Market Effects of Immigrant Legalization

Taking advantage of the ability to identify immigrants who were unauthorized to work prior to obtaining Legal Permanent Resident status, we use the New Immigrant Survey to examine whether lacking legal status to work in the U.S. constrains employment outcomes of illegal immigrants. With the exception of high-skilled unauthorized immigrants, the data fail to reveal evidence of improved employment outcomes attributable to legal status. In light of evidence that unauthorized immigrants experienced increased wages as a result of receiving amnesty through the 1986 Immigration and Reform Control Act during the 1990s, we interpret the results as evidence of ineffective employer sanctions.unauthorized, illegal, undocumented, immigration, legalization, amnesty

Multinational Firms and Manufactured Exports from Developing Countries

Multinational firms have played an important role in leading the developing countries into world markets. Multinationals from the United States, Japan and Sweden have all increased their shares of LDC exports of manufactures since the mid-1960s or mid-1970s. Their importance was particularly notable in Latin America, while their role in the Asian NICs decreased. The comparative advantages of U.S. and Swedish multinationals' affiliates in developing countries resembled those of their home countries more than those of their host countries, while Japanese affiliates' exports are lore similar to those of their host countries. There are some cases in which the advantage of the multinationals as exporters seems to be that they are able to combine company comparative advantages with the location advantages of producing in the developing countries.

Rotation of a single acetylene molecule on Cu(001) by tunneling electrons in STM

We study the elementary processes behind one of the pioneering works on STM controlled reactions of single molecules [Stipe et al., Phys. Rev. Lett. 81, 1263 (1998)]. Using the Keldysh-Green function approach for the vibrational generation rate in combination with DFT calculations to obtain realistic parameters we reproduce the experimental rotation rate of an acetylene molecule on a Cu(100) surface as a function of bias voltage and tunneling current. This combined approach allows us to identify the reaction coordinate mode of the acetylene rotation and its anharmonic coupling with the C-H stretch mode. We show that three different elementary processes, the excitation of C-H stretch, the overtone ladder climbing of the hindered rotational mode, and the combination band excitation together explain the rotation of the acetylene molecule on Cu(100).Comment: 5+5 pages, 4+2 figure

Outward FDI and Parent Exports and Employment: Japan, the United States, and Sweden

Within Japanese multinational firms, parent exports from Japan to a foreign region are positively related to production in that region by affiliates of that parent, given the parent's home production in Japan and the region's size and income level. This relationship is similar to that found for Swedish and U.S. multinationals in parallel studies. A Japanese parent's worldwide exports tend to be larger, relative to its output, the larger the firm's overseas production. In this respect also, Japanese firms resembled U.S. multinationals. A Japanese parent's employment, given the level of its production, tends to be higher, the greater the production abroad by the firm's foreign affiliates. Japanese firms' behavior in this respect is similar to that of Swedish firms, but contrasts with that of U.S. firms. U.S. firms appear to reduce employment at home, relative to production, by allocating labor-intensive parts of their production to affiliates in developing countries. Swedish firms seem to allocate the more capital-intensive parts of their production to their foreign affiliates, mostly in high-wage countries. We conclude that in Japanese firms and ancillary employment at home to service foreign operations outweighs any allocation of labor-intensive production to developing countries.