Valid Instrumental Variables Selection Methods using Auxiliary Variable and Constructing Efficient Estimator

In observational studies, we are usually interested in estimating causal effects between treatments and outcomes. When some covariates are not observed, an unbiased estimator usually cannot be obtained. In this paper, we focus on instrumental variable (IV) methods. By using IVs, an unbiased estimator for causal effects can be estimated even if there exists some unmeasured covariates. Constructing a linear combination of IVs solves weak IV problems, however, there are risks estimating biased causal effects by including some invalid IVs. In this paper, we use Negative Control Outcomes as auxiliary variables to select valid IVs. By using NCOs, there are no necessity to specify not only the set of valid IVs but also invalid one in advance: this point is different from previous methods. We prove that the estimated causal effects has the same asymptotic variance as the estimator using Generalized Method of Moments that has the semiparametric efficiency. Also, we confirm properties of our method and previous methods through simulations

Simple Robust Estimating Method for Propensity Score Models and its Application to Some Causal Estimands

To estimate causal effects accurately, adjusting covariates is one of the important steps in observational study. When all covariates are observed, the covariates can be adjusted, and an unbiased estimator for causal effects can be obtained. In this situation, the propensity score has the central role to estimate the causal effects. Recently, some causal estimands, the target population of causal effects estimation, are considered which depend on the "true" propensity score. A point to note that an interested estimands might have some bias if a propensity score model was misspecified. In this paper, we consider a multiply robust estimator for the propensity score. In brief, we prepare some candidate models, and construct an estimating equation including the candidate models at once. Some theoretical properties are proved, and we consider application examples for propensity score estimations when the average treatment effects for the overlap population is central interest.Comment: Keywords: Causal inference, Overlap weight, Propensity score, Robust estimatio

Evaluating the Conservativeness of Robust Sandwich Variance Estimator in Weighted Average Treatment Effects

In causal inference, the Inverse Probability Weighting (IPW) estimator is commonly used to estimate causal effects for estimands within the class of Weighted Average Treatment Effect (WATE). When constructing confidence intervals (CIs), robust sandwich variance estimators are frequently used for practical reasons. Although these estimators are easy to calculate using widely-used statistical software, they often yield narrow CIs for commonly applied estimands, such as the Average Treatment Effect on the Treated and the Average Treatment Effect for the Overlap Populations. In this manuscript, we reexamine the asymptotic variance of the IPW estimator and clarify the conditions under which CIs derived from the sandwich variance estimator are conservative. Additionally, we propose new criteria to assess the conservativeness of CIs. The results of this investigation are validated through simulation experiments and real data analysis.Comment: Keywords: Balancing weight, Causal estimands, Causal null hypothesis, Inverse probability weighting, Propensity scor

Pathophysiological roles of microvascular alterations in pulmonary inflammatory diseases: possible implications of tumor necrosis factor-alpha and CXC chemokines

Chronic obstructive pulmonary disease (COPD) and bronchial asthma are common respiratory diseases that are caused by chronic inflammation of the airways. Although these diseases are mediated by substantially distinct immunological reactions, especially in mild cases, they both show increased numbers of neutrophils, increased production of tumor necrosis factor-alpha (TNF-α) and poor responses to corticosteroids, particularly in patients with severe diseases. These immunological alterations may contribute strongly to airway structural changes, commonly referred to as airway remodeling. Microvascular alterations, a component of airway remodeling and caused by chronic inflammation, are observed and appear to be clinically involved in both diseases. It has been well established that vascular endothelial growth factor (VEGF) plays important roles in the airway microvascular alterations in mild and moderate cases of both diseases, but any role that VEGF might play in severe cases of these diseases remains unclear. Here, we review recent research findings, including our own data, and discuss the possibility that TNF-α and its associated CXC chemokines play roles in microvascular alterations that are even more crucial than those of VEGF in patients with severe COPD or asthma

Observation of Amplitude Mode Under Dc Electric Field in Smectic-cα* Phase

Linear and nonlinear dielectric spectroscopy under DC electric fields has been performed in the high temperature region of smectic-Cα* phase of an antiferroelectric liquid crystal 4-(1-methylheptyloxycarbonyl) phenyl 4-octylcarbonyloxybiphenyl-4-carboxylate (MHPOCBC) to obtain a deeper insight of dynamic properties. It is observed a softening of amplitude mode and ferroelectric mode with increasing the DC field close to the smectic-Cα*-smectic-A(C) phase boundary line. It was seen that the relaxation frequency of the amplitude mode obeys the Curie-Weiss law with respect to the applied electric field

Dielectric Propertiesof Smectic-cα* Phase

DIELECTRIC PROPERTIESOF SMECTIC-Cα* PHASE. Linear and third-order nonlinear dielectric measurements have been performed within the smectic-Cα* phase of antiferroelectric liquid crystal 4-(1-methyl-heptyloxycarbonyl) phenyl 4-octylcarbonyloxybiphenyl-4-carboxylate (MHPOCBC). In the low temperature region of smectic-Cα* phase, we observed the hysteresis of dielectric constant in cooling and heating process measurement. From the frequency dispersion measurement, it has been found that the frequency relaxation of antiferroelectric Goldstone mode and ‘low frequency mode', decreased with increasing the temperature until approach the center of the smectic-Cα* phase