Bayesian time series analysis of periodic behaviour and spectral structure

Analysis, model selection and forecasting in univariate time series models can be routinely carried out for models in which the model order is relatively small. Under an ARMA assumption, classical estimation, model selection and forecasting can be routinely implemented with the Box–Jenkins time domain representation. However, this approach becomes at best prohibitive and at worst impossible when the model order is high. In particular, the standard assumption of stationarity imposes constraints on the parameter space that are increasingly complex. One solution within the pure AR domain is the latent root factorization in which the characteristic polynomial of the AR model is factorized in the complex domain, and where inference questions of interest and their solution are expressed in terms of the implied (reciprocal) complex roots; by allowing for unit roots, this factorization can identify any sustained periodic components. In this paper, as an alternative to identifying periodic behaviour, we concentrate on frequency domain inference and parameterize the spectrum in terms of the reciprocal roots, and, in addition, incorporate Gegenbauer components. We discuss a Bayesian solution to the various inference problems associated with model selection involving a Markov chain Monte Carlo (MCMC) analysis. One key development presented is a new approach to forecasting that utilizes a Metropolis step to obtain predictions in the time domain even though inference is being carried out in the frequency domain. This approach provides a more complete Bayesian solution to forecasting for ARMA models than the traditional approach that truncates the infinite AR representation, and extends naturally to Gegenbauer ARMA and fractionally differenced models.     

半导体照明产品检测实验室建设及展望

基于半导体照明灯具的特点,结合目前半导体照明产品检测的实际情况,从光、色、电、寿命及安全性等方面介绍了半导体照明产品检测实验室的建设方案,包括系统的功能、组成、基本的检测原理和方法等。     

Determinants of consumer demand for circular economy products. A case for reuse and remanufacturing for sustainable development

We investigate determinants of consumer demand for circular (reused and remanufactured) products. Based on exploratory choice-based conjoint experiments with a sample of 800 adults in the United Kingdom, we examine two types of premium segment electronic appliances: a mobile phone and a robot vacuum cleaner. We find that consumers prefer partly circulated products over fully or not at all circulated products and that circular products can likely successfully enter the existing market at the retail price of a new product. Interestingly, circular products compete for market share primarily with new products, leaving the market share of second-hand options less affected. The results show a promising path for firms considering a transition to circular business models.     

A play-the-winner-type urn design with reduced variability

We propose a new adaptive allocation rule, the drop-the-loser, that randomizes subjects in the course of a trial comparing treatments with dichotomous outcomes. The rule tends to assign more patients to better treatments with the same limiting proportion as the randomized play-the-winner rule. The new design has significantly less variable allocation proportion than the randomized play-the-winner rule. Decrease in variability translates into a gain in statistical power. For some values of success probabilities the drop-the-loser rule has a double advantage over conventional equal allocation in that it has better power and assigns more subjects to the better treatment. Acknowledgments. I thank Stephen Durham, the associate editor, and the referees for their helpful suggestions.     

Dynamic contracting under imperfect public information and asymmetric beliefs

We develop a dynamic principal–agent model to show how imperfect public information and asymmetric beliefs about payoff-relevant parameters, agency conflicts, and the agent's implicit incentives to influence the principal's posterior beliefs through his unobservable actions interact to affect optimal dynamic contracts. We make a methodological contribution to the literature by solving the continuous-time contracting problem using a discrete-time approximation approach. We obtain a simple characterization of optimal renegotiation-proof contracts in terms of the solution to a nonlinear ordinary differential equation (ODE). We then exploit the properties of the ODE to derive a number of novel implications for the dynamics of long-term contracts that alter the intuition gleaned from the previous literature. Optimism has a first-order impact on incentives, investment and output that could reconcile the “private equity” puzzle. Consistent with empirical evidence, the interaction between asymmetric beliefs, risk-sharing and adverse selection costs could cause the time-paths of the agent's incentive intensities to be increasing or decreasing. Our results also suggest that the incorporation of imperfect public information and asymmetric beliefs could potentially reconcile empirical evidence of an ambiguous relation between risk and incentives, and a non-monotonic relation between firm value and incentives. Permanent and transitory components of risk have differing effects on incentives, which suggest that empirical investigations of the link between risk and incentives should appropriately account for different components of risk.     

Evaluation of medical costs associated with use of new oral anticoagulants compared with standard therapy among venous thromboembolism patients

Objective:

This study evaluated differences in medical costs associated with clinical end-points from randomized clinical trials that compared the new oral anticoagulants (NOACs), dabigatran, rivaroxaban, apixaban, and edoxaban, to standard therapy for treatment of patients with venous thromboembolism (VTE).

Research design and methods:

Event rates of efficacy and safety end-points from the clinical trials (RE-COVER, RE-COVER II, EINSTEIN-Pooled, AMPLIFY, Hokusai-VTE trial) were obtained from published literature. Incremental annual medical costs among patients with clinical events from a US payer perspective were obtained from the literature or healthcare claims databases and inflation adjusted to 2013 costs. Differences in total medical costs associated with clinical end-points for the NOACs vs standard therapy were then estimated. One-way and Monte Carlo sensitivity analyses were carried out.

Results:

A lower rate of major bleedings was associated with use of any of the NOACs vs standard therapy. Except for dabigatran, use of NOACs was also associated with a lower rate of recurrent VTE/death. As a result of the reduction in clinical event rates, the overall medical cost differences were ?$146, ?$482, ?$918, and ?$344 for VTE patients treated with dabigatran, rivaroxaban, apixaban, and edoxaban, respectively, vs patients treated with standard therapy.

Conclusions:

When any of the four NOACs are used instead of standard therapy for acute VTE, treatment medical costs are reduced. Apixaban is associated with the greatest reduction in medical costs, which is driven by medical cost reductions associated with both efficacy and safety end-points. Further evaluation may be needed to validate these results in the real-world setting.     

The new exchange rate policy in the Asian emerging economies – goodbye trouble,hello comfort?

In this paper, we discuss new aspects of exchange rate policy that can be observed in the Asian emerging economies. In the first place, we show the alternative regimes they may choose and their respective pros and cons. Secondly, we concentrate on the recent strategy of systematic undervaluation of one's currency – figuring prominently among ‘big’ Asian players such as China and India – and the most likely implications of such a strategy for domestic allocation, distribution and stabilization goals. With the background of Germany's experiences in 1969, almost on the eve of the Bretton Woods' system collapse, we model a speculative attack on an undervalued currency in the vein of the Flood–Garber seminal paper from 1984. Now, however, the country in concern (just like India and China) possesses strong rather than weak fundamentals. The continuous accumulation of international reserves, in addition, leads to the question of an ‘optimal management’ of foreign exchange reserves in Asian emerging economies with regard to size and composition. We finally propose a sequence of reforms/policies that should be implemented in those Asian emerging economies on their still long journey to a regime featured by autonomous monetary policy, flexible exchange rate and capital mobility. A brief summary and an outlook for future research close the paper.     

Does the law of one price hold in a high-inflation environment? A tale of two cities in Turkey

This study addresses the price convergence in two cities in Turkey (Istanbul and Ankara) using annual data over the three-quarters of the twentieth century (1922–1998), characterized by prevailing high inflation rates for most of the period. In contrast to the rest of the literature addressing convergence in price levels with a typical result of extremely slow convergence rates at best, we argue that convergence is much easier detected in growth rates rather than levels of prices. We suggest using the bounds testing procedure of Pesaran et al. (2001) for this purpose. We find a clear-cut evidence on the existence of a common driving force behind inflation dynamics in Istanbul and Ankara – a finding that is in contrast with the results typically reported in related literature.     

Diagnostics cannot have much power against general alternatives

Model diagnostics are shown to have little power unless alternative hypotheses can be narrowly defined. For example, the independence of observations cannot be tested against general forms of dependence. Thus, the basic assumptions in regression models cannot be inferred from the data. Equally, the proportionality assumption in proportional-hazards models is not testable. Specification error is a primary source of uncertainty in forecasting, and this uncertainty will be difficult to resolve without external calibration. Model-based causal inference is even more problematic.     

NFC协议的模糊测试优化方案

针对NFC协议进行模糊测试方案时产生大量不符合协议规范的无效测试用例而导致测试效率较低的问题,应用图论思想,提出了基于生成的策略与深度优先算法融合后的模糊测试方案。在基于生成的策略下构造测试用例的过程中,遍历由协议规范连接成的测试需求图,以深度优先算法搜索图中覆盖点较多的生成路径,精简测试用例的生成路径,保证生成的测试用例能够接近协议规范。实验分析表明,所提出的模糊测试方案能够有效地减少无效测试用例的生成,提高测试效率。