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

The Export Performance of Swedish and U.S. Multinationals

While the U.S. and Sweden both lost more than 20 per cent of their shares of world and developed countries' exports of manufactures over the 15 years or so after the mid-1960's, the export shares of their multinational firms stayed fairly stable or even increased. The multinationals, while first increasing and then holding fairly constant their shares of exports by their home countries, raised the proportion of their worldwide exports that they supplied from their overseas affiliates. These developments suggest that the declining trade shares of the U.S. and Sweden were not due mainly to deterioration in the innovativeness or inventiveness of American and Swedish firms or declines in their management ability or in their technological capabilities, but rather to economic developments in the firms' home countries. The finding that firms have done better as exporters than their home countries 4s strengthened when we look at different industry groups. In both the U.S. and Sweden, and in all industry groups, with one exception, the multinationals' export shares increased relative to those of their home countries. The margins were often wide, and were mostly larger for Swedish firms than for U.S. firms. In general, though the basic story was quite similar for the U.S. and Sweden, there were some notable differences. One was that the share of exports originating in affiliates was lower for Sweden than for the U.S. To a large extent, this difference in the siting of export production reflected the much greater export orientation of Swedish parents relative to U.S. parents, presumably a consequence of the relatively small size of the Swedish domestic market. Another difference between U.S. and Swedish multinationals was that while the U.S. firms' share in world manufacturing exports remained stable over the studied period, the Swedish firms' share rose by 14 per cent. We are so far not in a position to say whether this was because Swedish firms increased their competitiveness more than U.S. firms or because there was a higher conversion of Swedish firms into multinational status.

U.S. Firms in Latin American Service Industries

The participation of U.S. service industry firms in Latin American markets for services consists mainly of the activities of U.S.-owned affiliates operating in Latin America and very little of direct exports of ser- vices from the U.S. The important policy issues thus involve barriers to the establishment and operation of affiliates in host countries rather than trade barriers. Since direct investment rather than trade is at issue, the comparative advantages that are important are those of U.S. multinational firms rather than those of the U.S. as a country. The characteristics we observe in U.S. multinationals in these industries, particularly their low R & D intensity, are not those usually associated with the comparative advantages of U.S. multinationals. However, their skill intensity is relatively high. A more detailed breakdown of the sector does show at least some industries, particularly in finance, in which skill levels are very high, and these are the most likely candidates for major gains for U.S. multinationals. Nevertheless, U.S. shares in the Latin American service sector are very small overall and not likely to reach the levels in manufacturing or petroleum in the foreseeable future.

Analysis of error growth and stability for the numerical integration of the equations of chemical kinetics

Error growth and stability analyzed for numerical integration of differential equations in chemical kinetic

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

Identifying stochastic oscillations in single-cell live imaging time series using Gaussian processes

Multiple biological processes are driven by oscillatory gene expression at different time scales. Pulsatile dynamics are thought to be widespread, and single-cell live imaging of gene expression has lead to a surge of dynamic, possibly oscillatory, data for different gene networks. However, the regulation of gene expression at the level of an individual cell involves reactions between finite numbers of molecules, and this can result in inherent randomness in expression dynamics, which blurs the boundaries between aperiodic fluctuations and noisy oscillators. Thus, there is an acute need for an objective statistical method for classifying whether an experimentally derived noisy time series is periodic. Here we present a new data analysis method that combines mechanistic stochastic modelling with the powerful methods of non-parametric regression with Gaussian processes. Our method can distinguish oscillatory gene expression from random fluctuations of non-oscillatory expression in single-cell time series, despite peak-to-peak variability in period and amplitude of single-cell oscillations. We show that our method outperforms the Lomb-Scargle periodogram in successfully classifying cells as oscillatory or non-oscillatory in data simulated from a simple genetic oscillator model and in experimental data. Analysis of bioluminescent live cell imaging shows a significantly greater number of oscillatory cells when luciferase is driven by a {\it Hes1} promoter (10/19), which has previously been reported to oscillate, than the constitutive MoMuLV 5' LTR (MMLV) promoter (0/25). The method can be applied to data from any gene network to both quantify the proportion of oscillating cells within a population and to measure the period and quality of oscillations. It is publicly available as a MATLAB package.Comment: 36 pages, 17 figure

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

FDI in the Restructuring of the Japanese Economy

This paper examines how inward and outward foreign direct investment (FDI) have influenced the restructuring of the Japanese economy and can be expected to continue to do so in the future. We find that outward investment has helped Japanese firms to sustain foreign market shares and contributed to the restructuring of the Japanese economy away from older industries. By shifting from exporting to affiliate production, there has been a geographical reallocation of the activities of Japanese firms, particularly those of multinational manufacturing firms. However, Japanese outward FDI is still not very large relative to the Japanese economy, despite the rapid growth since the mid-1980s, and there is still scope for significant increase when compared with the levels of most other OECD countries. Inward FDI will presumably have an even stronger impact on the restructuring of the Japanese economy. Although the stock of inward foreign direct investment is still very small, there are important changes under way. Deregulation has opened up much of the industrial and service sectors to foreign multinationals.

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.