Combining the minimum-variance and equally-weighted portfolios: Can portfolio performance be improved?

It is documented in the literature that due to estimation errors, mean-variance efficient portfolios deliver no higher out-of-sample Sharpe ratios than does the naïve equally-weighted portfolio (EWP). This paper demonstrates how the out-of-sample performance of the minimum-variance portfolio (MVP) can be improved in the presence of estimation errors by combining the MVP and EWP. Our results indicate that an appropriate combination of the MVP and EWP can enhance Sharpe ratios under any scenarios considered, and can also reduce the portfolio risk if short-selling is allowed. However, the combination strategy is not able to generate a lower risk level than the MVP when a short-selling restriction is imposed. We find that the optimal combination coefficient depends on the factors that greatly impact estimation errors in the MVP, including sample size, estimation method, no-short-selling restriction, and length of the out-of-sample period under consideration.     

The accuracy of interest rate forecasts in the Asia-Pacific region: opportunities for portfolio management

We analysed interest rate forecasts from Australia, China, Hong Kong, India, Indonesia, Malaysia, New Zealand, Singapore, South Korea, Taiwan and Thailand. We assessed 532 forecast time series with a total of 85,264 individual interest rate forecasts. To do so, we carried out a comparison to naïve forecasts and investigated the forecast time series for topically orientated trend adjustments. In addition, we deployed the sign accuracy test and the unbiasedness test. The results are very sobering in part: 95.9% of all forecast time series are characterized by the phenomenon of topically orientated trend adjustments, and 99.4% of all forecast time series proved to be biased. Only a small proportion of the forecast time series (3.6%) reflected the future interest rate trend significantly more precisely than a naïve forecast. However, at the same time some of the results of the study are surprisingly positive. The sign accuracy test revealed that 48.3% of all forecast time series predict the interest rate trend significantly better than a random walk forecast.     

Time-inconsistent preferences in a general equilibrium model

This paper introduces time-inconsistent preferences in a multicommodity general equilibrium framework with incomplete markets. The standard concept of competitive equilibrium is extended in order to allow for changes in intertemporal preferences. Depending on whether or not agents recognize that their intertemporal preferences change, agents are called sophisticated or naïve. This paper presents competitive equilibrium notions for economies with naïve agents and economies with sophisticated agents and provides assumptions under which both types of equilibria exist. Surprisingly, the set of naïve equilibria in societies populated by time-consistent households is not allocationally equivalent to the set of competitive equilibria. For sophisticated equilibria, the equivalence holds. Time-inconsistency also raises conceptual issues about the appropriate concept of efficiency. Choices have to be made concerning the incorporation of future preferences and the appropriate instruments to create Pareto improvements. For both naïve and sophisticated societies, we present four possible efficiency concepts. Suitable conditions are specified for which both naïve and sophisticated equilibria satisfy appropriate efficiency concepts.     

Trade,Growth, and Increasing Returns to Infrastructure: The Role of the Sophisticated Monopolist*

Equilibrium in international trade with increasing returns in infrastructure depends on whether the infrastructure provider is “naïve” or sophisticated. A monopolist produces infrastructure under decreasing cost using fixed equipment. Unlike similar work, we derive a unique closed‐economy equilibrium. In a small open economy, with “naïve” infrastructure provider(s), multiple equilibria obtain. The industrial export potential of the economy depends on unexhausted economies of scale, and equilibria are possible where manufactures are exported despite an autarky price higher than the world price. With a sophisticated infrastructure provider, even an open economy has a unique equilibrium, which, at least as long as economies of scale are unexhausted, also involves more industrialization than the “naïve” equilibria. Access to the unlimited world market is necessary for significant industrialization but is not sufficient: one may also require “Schumpeterian” entrepreneurs, monopolists with a panoramic vision of the economy and of their catalytic role in it.     

Financial diversification before modern portfolio theory: UK financial advice documents in the late nineteenth and the beginning of the twentieth century

Abstract

The paper offers textual evidence from a series of financial advice documents in the late nineteenth century and the early twentieth century of how UK investors perceived of and managed risk. In the world's largest financial centre of the time, UK investors were familiar with the concept of correlation and financial advisers’ suggestions were consistent with the recommendations of modern portfolio theory in relation to portfolio selection strategies. From the 1870s, there was an increased awareness of the benefits of financial diversification – primarily putting equal amounts into a number of different securities – with much of the emphasis being on geographical rather than sectoral diversification and some discussion of avoiding highly correlated investments. Investors in the past were not so naïve as mainstream financial discussions suggest today.     

El Niño and La Niña induced volatility spillover effects in the U.S. soybean and water equity markets

This paper examined links between U.S. soybean prices and the Dow Jones U.S. Water Index (DJUSWU). We particularly studied the impact of El Niño and La Niña events on price risk spillovers. Results showed that La Niña significantly increases the linkages between soybean and water equity markets. Based on this, we identified a new soybean hedge strategy that would be possible if a futures contract for the DJUSWU existed. This new strategy improves on the effectiveness of both a conventional naïve soybean market hedge, and a traditional time-varying hedge. The findings can be used to assist soybean agents in managing increased market risks associated with extreme weather events.     

Public Goods,Social Norms,and Naïve Beliefs

An individual's contribution to a public good may be seen by others as a signal of attributes such as generosity or wealth. An individual may, therefore, choose their contribution so as to send an appropriate signal to others. In this paper, we question how the inferences made by others will influence the amount contributed to the public good. Evidence suggests that individuals are naïve and biased toward taking things at “face value.” We contrast, therefore, contributions made to a public good if others are expected to make rational inferences versus contributions if others are expected to make naïve inferences.     

Passive learning: a critique by example

In models of learning by experimentation that exhibit signal dependence, a benchmark using a passive learner has been proposed. The use of this benchmark is flawed – first, passive learning does not disentangle the effects of knowing that beliefs, as well as other state variables, might change, and we address this issue directly by introducing a naïve learner. Secondly, and more tellingly, passive learning does not do what it is supposed to do, namely help measure the gains from active experimentation; the naïve learner enables us to illustrate this point in the context of a particular example.     

A comprehensive study on smart beta strategies in the A-share market

In this article, we explore how smart beta strategies are applied in the Chinese A-share market. Specifically, we empirically examine several popular smart beta strategies, including mean-variance optimization, minimum-variance portfolio, equal weighting, risk parity strategy, and fundamental indexation, and we do so using the Shanghai Stock Exchange (SSE) 50 index and SSE sector indices as our comparison benchmarks. We find that all smart beta strategies outperform these benchmarks from year 2006 to year 2015, and that all smart beta strategies outperform the SSE 50 index by an average of 2.57% per year. In turn, these strategies improve the Sharpe Ratio by 46.2% on average.     

Out‐of‐Sample Exchange Rate Forecasting and Macroeconomic Fundamentals: The Case of Japan

This study explores the respective out‐of‐sample exchange rate forecasting abilities of five macroeconomic fundamental models in comparison to a naïve random walk model for Japan during the post‐Bretton Woods era. To assess the influence of major economic changes, we estimate both linear and nonlinear models for all the macroeconomic fundamentals. Overall, most structural exchange rate models outperform a naïve random walk model in terms of forecasting accuracy in the short horizon. When the fundamentals are only linearly modelled, the forecasting ability of the Taylor rule is generally superior to other fundamental models. When the fundamentals are nonlinearly specified, the predictability of some other models rises dramatically to match that of the Taylor rule models in short and/or long horizons. Of importance, we determine that the yen/dollar exchange rate forecasting performance effectively improves in several fundamental models when influential economic changes are incorporated.     

Hyperbolic Discounting,Borrowing Aversion and Debt Holding

Analysis of an original Internet‐based survey reveals that debt holding is related to time discounting through: (i) present bias, measured by the degree of declining impatience in the generalized hyperbolic discount function; (ii) borrowing aversion, captured by a sign effect in that future losses are discounted at lower rates than future gains; and (iii) impatience, measured by the overall discount rate. Hyperbolic respondents are classified naïve if their answers reveal them to be time‐inconsistent procrastinators, and otherwise sophisticated. Naïve respondents with more steeply declining impatience are more likely to be debtors. The sign effect relates negatively to borrowing. Survey responses indicative of high or declining impatience are associated with credit card borrowing and other overborrowing indicators.     

An economic evaluation of tofacitinib for the treatment of moderately-to-severely active ulcerative colitis: modeling the cost of treatment strategies in the United States

Abstract

Aims: To evaluate the cost differences between a treatment strategy including tofacitinib (TOFA) vs treatment strategies including adalimumab (ADA), golimumab (GOL), infliximab (IFX), and vedolizumab (VEDO) among all patients with moderate-to-severe ulcerative colitis (UC) (further stratified by patients naïve/exposed to tumor necrosis factor inhibitors [TNFis]).

Materials and methods: An Excel-based decision-analytic model was developed to evaluate costs from the perspective of a third-party US payer over 2 years. Efficacy and safety parameters were taken from prescribing information and published trials. All patients started induction therapy on the first treatment in the strategy and continued if efficacy criteria were met and no major adverse event occurred (in which cases they proceeded to the next treatment in the strategy).

Results: The cost per member per month (PMPM) of the TOFA–>IFX–>VEDO–>GOL strategy ($1.11) was lower than that of the ADA–>IFX–>VEDO–>GOL strategy ($1.34; Δ = $?0.23) among the TNFi-naïve population (n?=?204 patients out of a plan of one million members). Similarly, the use of TOFA before ADA (i.e. TOFA–>ADA–>IFX–> VEDO) was also associated with lower PMPM costs than the use of ADA before TOFA (i.e. ADA–>TOFA–>IFX–>VEDO): $1.15 vs $1.25 (Δ = $?0.10). Similar, and often larger, differences were observed in both the overall moderate-to-severe population and the TNFi-exposed population. Sensitivity analyses resulted in the same conclusions.

Limitations: Our model relied on efficacy data from prescribing information and published trials, which were not head-to-head and slightly differed with respect to methods. Additionally, our model used representative minor and major ADRs (and the associated costs) to represent toxicity management, which was a simplifying assumption.

Conclusions: This analysis, the first of its kind to evaluate TOFA vis-à-vis other advanced therapies in the US, suggests the early use of TOFA among both TNFi-naïve and TNFi-failure patients results in lower PMPM costs compared with other treatment alternatives.     

On mean-variance portfolio selection under a hidden Markovian regime-switching model

We study a mean-variance portfolio selection problem under a hidden Markovian regime-switching Black–Scholes–Merton economy. Under this model, the appreciation rate of a risky share is modulated by a continuous-time, finite-state hidden Markov chain whose states represent different states of an economy. We consider the general situation where an economic agent cannot observe the “true” state of the underlying economy and wishes to minimize the variance of the terminal wealth for a fixed level of expected terminal wealth with access only to information about the price processes. By exploiting the separation principle, we discuss the mean-variance portfolio selection problem and the filtering-estimation problem separately. We determine an explicit solution to the mean-variance problem using the stochastic maximum principle so that we do not need the assumption of Markovian controls. We also provide robust estimates of the hidden state of the chain and develop a robust filter-based EM algorithm for online recursive estimates of the unknown parameters in the model. This simplifies the filtering-estimation problem.     

Present-biased preferences,self-awareness and shirking

We model a mechanism design problem in which the principal owns a project that requires work effort by an agent, but agents may have time-inconsistent, present-biased preferences and lack complete self-awareness of these preferences. The self-control problem and naïveté of an agent may lead him to agree to a contract but later shirk or slack-off, even though doing so is observable. When the principal cannot severely punish shirking and agents are completely naïve, the second-best solution entails allowing a present-biased agent to slack-off in order to avoid a greater loss due to shirking. With greater self-awareness among present-biased agents, the principal may do better by screening some from accepting the contract. Furthermore, when shirking can be severely punished, this does not lead to contracts that eliminate effects of the self control problem. Instead the principal may exploit present-biased agents by offering a contract that allows them to slack-off (which agents fail to foresee they will choose to do) but at the expense of foregoing much compensation.     

No trade

We investigate a common value bilateral bargaining model with two-sided private information and no aggregate uncertainty. A seller owns an asset whose common valuation is a deterministic function of the two traders' private signals. We first establish a no-trade theorem for this environment, and proceed to study the effect of the asset valuation structure and the trading mechanism on extent to which asymmetric information induces individuals to engage in mutually unprofitable exchange. A laboratory experiment is conducted, where trade is found to occur between 19% and 35% of the time, and this depends in systematic ways on both the asset valuation function and the trading mechanism. Both buyers and sellers adapt their strategy to changes in the asset valuation function and to changes in the trading mechanism in clearly identifiable ways. An equilibrium model with naïve belief formation accounts for some of the behavioral findings, but open questions remain.     

Exact arbitrage and portfolio analysis in large asset markets

Summary. We provide a detailed portfolio analysis for a financial market with an atomless continuum of assets. In the context of an exact arbitrage pricing theory (EAPT), we go beyond the characterization of the existence of important portfolios (normalized riskless, mean, cost, factor and mean-variance efficient portfolios) to furnish exact portfolio compositions in terms of explicit portfolio weights. Such an analysis has not been furnished before in the context of the asymptotic arbitrage pricing theory (APT). We also characterize conditions under which a mean-variance efficient portfolio is a benchmark portfolio used in the EAPT to proxy essential risk. We illustrate our results with several examples of specific financial markets. Received: May 30, 2002; revised version: August 15, 2002 RID="*" ID="*"Some of the results reported here constituted part of Cowles Foundation Discussion Paper– No. 1139 circulated under the title “Hyperfinite Asset Pricing Theory”; additional results were obtained when Sun visited the Department of Economics at Johns Hopkins University during March 2002. This paper was presented at the Conference on Economic Design held at NYU on July 6–9, 2002 Correspondence to: M. A. Khan     

Strategy-proofness in experimental matching markets

We introduce two novel matching mechanisms, Reverse Top Trading Cycles (RTTC) and Reverse Deferred Acceptance (RDA), with the purpose of challenging the idea that the theoretical property of strategy-proofness induces high rates of truth-telling in economic experiments. RTTC and RDA are identical to the celebrated Top Trading Cycles (TTC) and Deferred Acceptance (DA) mechanisms, respectively, in all their theoretical properties except that their dominant-strategy equilibrium is to report one’s preferences in the order opposite to the way they were induced. With the focal truth-telling strategy being out of equilibrium, we are able to perform a clear measurement of how much of the truth-telling reported for strategy-proof mechanisms is compatible with rational behaviour and how much of it is caused by confused decision-makers following a default, focal strategy without understanding the structure of the game. In a school-allocation setting, we find that roughly half of the observed truth-telling under TTC and DA is the result of naïve (non-strategic) behaviour. Only 14–31% of the participants choose actions in RTTC and RDA that are compatible with rational behaviour. Furthermore, by looking at the responses of those seemingly rational participants in control tasks, it becomes clear that most lack a basic understanding of the incentives of the game. We argue that the use of a default option, confusion and other behavioural biases account for the vast majority of truthful play in both TTC and DA in laboratory experiments.

     

The evolution of portfolio rules and the capital asset pricing model

The aim of this paper is to test the performance of capital asset pricing model (CAPM) in an evolutionary framework. We model an economy where a heterogeneous population of long-lived agents invest their wealth according to different portfolio rules, and prove that traders who either “believe” in CAPM and use it as a rule of thumb, or are endowed with genuine mean-variance preferences, under some very weak conditions, vanish in the long run.We show that a sufficient condition to drive CAPM or mean-variance traders’ wealth shares to zero is that an investor endowed with a logarithmic utility function enters the market.     

Multi-period portfolio optimization under possibility measures

A single-period portfolio selection theory provides optimal tradeoff between the mean and the variance of the portfolio return for a future period. However, in a real investment process, the investment horizon is usually multi-period and the investor needs to rebalance his position from time to time. Hence it is natural to extend the single-period fuzzy portfolio selection to the multi-period case based on the possibility theory. In this paper, we propose the possibilistic expected value and variance for the terminal wealth with fuzzy forms after T periods by using the central value operator. Classes of multi-period possibilistic mean-variance models are formulated originally under the assumption that the proceeds of risky assets are fuzzy variables. Besides, we apply a particle swarm optimization algorithm to solve the proposed multi-period fuzzy portfolio selection models. A numerical example is given to illustrate the performance of the proposed models and algorithm.     

Predictors for total hospital and cardiology cost claims among patients with atrial fibrillation initiating dabigatran or acenocoumarol in The Netherlands

Aims: The prevalence of atrial fibrillation (AF) has increased over the past years due to aging of the population, and healthcare costs associated with AF reflect a significant financial burden. The aim of this study was to explore predictors for the real-world AF-related in-hospital costs in patients that recently initiated anticoagulation with acenocoumarol or dabigatran.

Methods: Predictors for claimed total hospital care costs and cardiology costs in AF patients were explored by using hospital financial claims data from propensity score matched patient groups in a large Dutch community hospital. This study analyzed the total dataset (n?=?766) and carried out a secondary analysis for all matched pairs of anticoagulation naïve AF patients (n?=?590) by ordinal regression.

Results: Dabigatran was a predictor for significantly lower cardiology and total hospital care costs (Odds Ratio [OR]?=?0.43, 95% confidence interval (CI)?=?0.33–0.57; and OR?=?0.60, 95% CI?=?0.46–0.79, respectively). Female gender was a predictor for lower total hospital care costs. Predictors for an increase in total hospital care costs were the occurrence of stroke or systemic embolism, major bleeding, and minor bleeding. The costs predictors were comparable when limiting the analysis to patients that were anticoagulation naïve. Age and CHA₂DS₂-VASc were not predictors for either cardiology or total hospital care costs in both analyses.

Conclusion: Dabigatran treatment was as a predictor for lower cardiology costs and lower total hospital care costs in AF patients that initiated oral anticoagulation.