This paper reviews the recent developments in the field of the variance-ratio tests of random walk and martingale hypothesis. In particular, we present the conventional individual and multiple VR tests as well as their improved modifications based on power-transformed statistics, rank and sign tests, subsampling and bootstrap methods, among others. We also re-examine the weak-form efficiency for five emerging equity markets in Latin America.

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A Monte Carlo experiment is conducted to compare power properties of alternative tests for the martingale difference hypothesis. Overall, we find that the wild bootstrap automatic variance ratio test shows the highest power against linear dependence; while the generalized spectral test performs most desirably under nonlinear dependence.

Financial market participants and policy-makers can benefit from a better understanding of how shocks can affect volatility over time. This study assesses the impact of structural changes and outliers on volatility persistence of three crude oil markets -Brent, West Texas Intermediate (WTI)

This paper compares the GDP forecasting performance of alternative factor models based on monthly time series for the French economy. These models are based on static and dynamic principal components obtained using time and frequency domain methods. We question whether it is more appropriate to use aggregate or disaggregate data to extract the factors used in forecasting equations. The forecasting accuracy is evaluated for various forecast horizons considering both rolling and recursive schemes. We empirically show that static factors, estimated from a small database, lead to competitive results, especially for nowcasting. Copyright © 2009 John Wiley & Sons, Ltd.

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International audienceThis paper contributes to the literature on the impact of the Shari'ah filtering criteria on the risk of Dow Jones Islamic indexes relative to their conventional counterparts. We show that Islamic and conventional indexes are affected by the same extreme events which can bias the estimation of the risk, especially the period of the Global Financial Crisis of 2007-2008 and its aftermath which is characterized by a very high level of volatility. Then, we examine whether the Islamic indexes are more risky than the conventional indexes using different risk measures. We also analyzed the performance of both indexes from various risk-adjusted performance measures. Overall, the Islamic indexes seem to be more risky than their conventional counterparts as well as exhibit a higher performance on the full period (1996-2013). The sample period is further divided into low volatility period and high volatility period based on the detection of structural breaks in the volatility. The results also show that both indexes have been affected by variance changes. We show that most of the Islamic indexes have higher level of risk than the conventional indexes, whatever the sub-periods. Consequently, this finding means that the Islamic indexes are riskier than the non-Islamic indexes. We also find that in most cases the Islamic indexes either outperform the non-Islamic indexes or there is no significant difference in performance between both indexes. These findings can be explained as a consequence of less diversification in Islamic indexes, leading to higher concentration risk in some sectors, such as basic material, industrial and technology firms. Further, we also fin