Identifying Demand with Multidimensional Unobservables: A Random Functions Approach

We explore the identification of nonseparable models without relying on the property that the model can be inverted in the econometric unobservables. In particular, we allow for infinite dimensional unobservables. In the context of a demand system, this allows each product to have multiple unobservables. We identify the distribution of demand both unconditional and conditional on market observables, which allows us to identify several quantities of economic interest such as the (conditional and unconditional) distributions of elasticities and the distribution of price effects following a merger. Our approach is based on a significant generalization of the linear in random coefficients model that only restricts the random functions to be analytic in the endogenous variables, which is satisfied by several standard demand models used in practice. We assume an (unknown) countable support for the the distribution of the infinite dimensional unobservables.

Connected Substitutes and Invertibility of Demand

We consider the invertibility of a nonparametric nonseparable demand system. Invertibility of demand is important in several contexts, including identification of demand, estimation of demand, testing of revealed preference, and economic theory requiring uniqueness of market clearing prices. We introduce the notion of "connected substitutes" and show that this structure is sufficient for invertibility. The connected substitutes conditions require weak substitution between all goods and sufficient strict substitution to necessitate treating them in a single demand system. These conditions are satisfied in many standard models, have transparent economic interpretation, and allow us to show invertibility without functional form restrictions, smoothness assumptions, or strong domain restrictions.Demand, Invertibility, Connected substitutes

Why a viable third party might lead to less negative political advertising in campaigns.

More than 80 percent of advertisements in political campaigns are negative; a type of messaging that is much less common in markets for consumer goods and services. Why is negativity so specific to political campaigns? In new research, Amit Gandhi, Daniela Iorio, and Carly Urban explain that the dual Democrat-Republican nature of US politics encourages candidates to go negative. They find that elections with two candidates are twice as likely to see negative ads compared to those with a greater number of candidates, and argue that the rise of a viable third party in the US might reduce the amount of attack advertising

Chemometric – assisted UV spectrophotometric method for determination of antihyperlipidemic agents in pharmaceutical formulation

This presented work is based on application of two multivariate calibration methods for simultaneous UV-VIS spectrophotometric determination of active substances in combined pharmaceutical formulation composed of Atorvastatin calcium (ATV) and Ezetimibe (EZT). The methods used were Principal Component Regression (PCR) and Partial Least Square (PLS). The Spectra of ATV and EZT were recorded at concentrations within their linear range 5.0-30.0 μg/ml for both drugs. 28 set of mixtures were used for calibration and 08 set of mixtures were used for validation in the wavelength range of 230 to 260 nm with the wavelength intervals λ= 0.5 nm in methanol. The methods were validated as per International Conference on HarmonizationQ2 (R1) (ICH) guidelines. These methods were successfully applied for determination of drugs in pharmaceutical formulation (tablet) with no interference of the excipient as indicated by the recovery study results. The proposed methods are simple, rapid and can be easily used as an alternative analysis tool in the quality control as well as in process control of drugs and formulation

Identifying Heterogeneity in Economic Choice Models

We show how to nonparametrically identify the distribution that characterizes heterogeneity among agents in a general class of structural choice models. We introduce an axiom that we term separability and prove that separability of a structural model ensures identification. The main strength of separability is that it makes verifying the identification of nonadditive models a tractable task because it is a condition that is stated directly in terms of the choice behavior of agents in the model. We use separability to prove several new results. We prove the identification of the distribution of random functions and marginal effects in a nonadditive regression model. We also identify the distribution of utility functions in the multinomial choice model. Finally, we extend 2SLS to have random functions in both the first and second stages. This instrumental variables strategy applies equally to multinomial choice models with endogeneity.

VITAMIN B6 METABOLISM AND REGULATION OF PYRIDOXAL KINASE

Pyridoxal 5\u27-phosphate (PLP) is the cofactor for over 140 vitamin B6 (PLP)-dependent enzymes that are involved in various metabolic and biosynthetic pathways. Pyridoxal kinase (PL kinase) and pyridoxine 5’-phosphate oxidase (PNP oxidase) are the two key enzymes that metabolize nutritional forms of vitamin B6, including pyridoxal (PL), pyridoxine (PN), and pyridoxamine (PM) to the active cofactor form, PLP. Disruption of the PLP metabolic pathway due to mutations in PNP oxidase or PL kinase result in PLP deficiency, which is implicated in several neurological pathologies. Several ingested compounds are also known to result in PLP deficiency with concomitant neurotoxic effects. How these mutations and compounds affect B6 metabolism is not clearly understood. On the other hand, an emerging health problem is the intake of too much vitamin B6 as high doses of the reactive PLP in the cell exhibits toxic effects, including sensory and motor neuropathies. The overall aim of this research is to understand the catalytic function of PL kinase and the regulatory pathway of PLP metabolism. Using site-directed mutagenesis (Asp235Asn, Asp235Ala), kinetic and structural studies, we have shown that Asp235 may play a catalytic role in PL kinase phosphorylation activity. We also show that human PL kinase binds its substrates, PL and MgATP synergistically, and that the enzyme requires Na+ (or K+) and Mg2+ for its activity. Using kinetic study, we show severe induced MgATP substrate inhibition of PL kinase in the presence of its product, PLP, and we postulate this to be due to the formation of a non-productive ternary complex (Enzyme•PLP•MgATP). Consistently, our crystal structure of human PL kinase (2.1 Å) co-crystallized with MgATP and PLP showed both MgATP and PLP trapped at the active site. Our hypothesis is that this abortive ternary complex might be a physiological process, and that PL kinase uses this mechanism to self-regulate its activity. Our inhibition studies show theophylline, a bronchodilator as a mixed competitive inhibitor of human PL kinase with Ki of 71 μM. Our structural study (2.1 Å) shows theophylline bound at the substrate, PL binding site of human PL kinase. We also identified several potential PL kinase inhibitors from the DrugBank Chemical Compound database. Some of these compounds, including enprofylline, theobromine, caffeine, and lamotrigine, which incidentally exhibit similar neurotoxic effects as theophylline, show significant inhibitory effect on human PL kinase. Further studies are also planned to investigate the effect of these drugs on vitamin B6 metabolism in vivo