A Simple Out-of-Sample Test of Predictability against the Random Walk Benchmark

We show that a straightforward modification of a trading-based test for predictability displays interesting advantages over the Excess Profitability (EP) test proposed by Anatolyev and Gerco when testing the Driftless Random Walk Hypothesis. Our statistic is called the Straightforward Excess Profitability (SEP) test, and it avoids the calculation of a term that under the null of no predictability should be zero but in practice may be sizable. In addition, our test does not require the strong assumption of independence used to derive the EP test. We claim that dependence is the rule and not the exception. We show via Monte Carlo simulations that the SEP test outperforms the EP test in terms of size and power. Finally, we illustrate the use of our test in an empirical application within the context of the commodity-currencies literature.

Random Walk Hypothesis for Stock Prices in Fiji

The main goal of this paper is to investigate the random walk hypothesis in Fiji using monthly data from January 2000 to October 2017. Applying augmented Dickey Fuller (ADF 1979, 1981) and Phillips-Perron (1988), Zivot-Andrews (1992), and Narayan and Popp (2010) unit root tests, this study finds that stock prices is best characterized as non-stationary. The estimated multiple structural break dates in the stock prices corresponds with devaluation of Fijian dollar by 20 percent in 2009 and General Elections in September 2014, which Fiji First Party won by majority votes. The empirical results indicate that stock prices are best characterized as a unit root (random walk) process, indicating that the weak-form efficient market hypothesis holds in Fiji’s stock market. Hence, it will be difficult to predict future returns based on historical movement of stock prices in Fiji’s stock market.

An Empirical Investigation of the Random Walk Hypothesis in the Nigerian Stock Market

The Random Walk Hypothesis (RWH) states that stock prices move randomly in the stock market without following any regular or particular pattern and as such historical information contained in the past prices of stocks cannot be used to predict current or future stock prices. Hence, stock prices are unpredictable and that investors cannot usurp any available information in the market to manipulate the market and make abnormal profits. This study empirically examines the random walk hypothesis in the Nigerian stock market using the daily quotations of the Nigerian stock exchange from 2nd January, 1998 to 31st December, 2019. The study employs Augmented Dickey-Fuller unit root test, the random walk model, Ljung-Box Q-statistic test for serial dependence, runs test of randomness, and the robust variance ratio test as methods of analyses. The result of the study rejected the null hypotheses of a unit root and random walk in the stock returns. The null hypothesis of no serial correlation in the residuals of stock returns was also rejected indicating the presence of serial correlation/autocorrelation in the residual series. The result of the runs test rejected the null hypothesis of randomness in the Nigerian stock returns. The results of the variance ratio test under homoskedasticity and heteroskedasticity assumptions both strongly rejected the null hypothesis of a random walk for both joint tests and test of individual periods. Based on the results of the four tests applied in this study, it is concluded that the Nigerian daily stock returns under the period of investigation do not follow a random walk and hence the null hypothesis of a random walk is rejected. The results of the study further revealed that the Nigerian stock market is weak-form inefficient indicating that prices in the Nigerian stock market are predictable, dependable, consistently mispriced, inflated, liable to arbitraging and left unprotected to speculations and market manipulations. The study provided some policy recommendations

APAKAH SAHAM FARMASI DI BURSA EFEK INDONESIA MENGIKUTI HIPOTESIS RANDOM WALK SAAT PANDEMI COVID-19?

<p><em><span lang="EN-US">Berbeda dengan saham lain yang turun cukup tajam saat dimulainya pandemi Covid-19, pergerakan harga saham farmasi justru mengalami peningkatan. Kenaikan harga saham farmasi sejalan dengan ekspektasi investor terhadap peningkatan permintaan obat dan suplemen kesehatan yang berdampak pada kenaikan harga saham di pasar. Penelitian ini secara empiris bertujuan untuk menguji perilaku rantai jual beli di Bursa Efek Indonesia (BEI) yaitu PT Indo Farma Tbk (INAF), PT Kimia Farma Tbk (KAEF), PT Kalbe Farma Tbk (KLBF), PT Phapros Tbk (PEHA), PT Pyridam Farma Tbk (PYFA), dan PT Tempo Scan Pacific Tbk (TSPC). Secara khusus, penelitian ini menyelidiki apakah akan melaporkan apakah saham farmasi selama Pandemi Covid-19 mengikuti Random Walk Hypothesis (RWH) atau sebaliknya apakah pergerakan harga dapat diprediksi. Data yang digunakan dalam penelitian ini adalah harga penutupan saham harian dari tanggal 2 Januari 2020 sampai dengan 2 Februari 2021. Data dianalisis menggunakan uji Augmented Dickey-Fuller untuk adanya Uji Unit Root, uji Variance Ratio, dan Autoregressive Moving Average. (ARMA). Hasilnya, berdasarkan Uji Akar Unit, semua data stasioner di tingkat. Pengujian lebih lanjut menggunakan Variance Ratio, baik secara stand alone intersep maupun trend dan antar semua data juga tidak bergerak secara acak dan tidak mengikuti Hipotesis Random Walk. Terakhir, dengan menggunakan model ARMA, pergerakan log return saham farmasi di BEI dapat diprediksi.</span></em></p><p><em><span lang="EN-US"><em><span>In contrast to other stocks that fell quite sharply at the start of the Covid-19 pandemic, pharmaceutical stock price movements have increased. The increase in the price of pharmaceutical stocks is in line with investors' expectations of an increase in demand for medicines and health supplements, which will have an impact on the increase in stock prices in the market. This study empirically aims to examine the behavior of the chain buying and selling on the Indonesia Stock Exchange (IDX), namely PT Indo Farma Tbk (INAF), PT Kimia Farma Tbk (KAEF), PT Kalbe Farma Tbk (KLBF), PT Phapros Tbk (PEHA), PT Pyridam Farma Tbk (PYFA), and PT Tempo Scan Pacific Tbk (TSPC). Specifically, this study investigates whether to report whether pharmaceutical stocks during the Covid-19 Pandemic followed the Random Walk Hypothesis (RWH) or vice versa whether the price movements were predictable. The data used in this study are daily stock closing prices from January 2, 2020, to February 2, 2021. The data were analyzed using the Augmented Dickey-Fuller test for the existence of the Unit Root Test, Variance Ratio test, and Autoregressive Moving Average (ARMA). The result, based on the Unit Root Test, all data is stationary at the level. Further testing using the Variance Ratio, both by stand-alone intercept and trend and between all data also does not move randomly and does not follow the Random Walk Hypothesis. Finally, using the ARMA model, the log return movement of pharmaceutical stocks in IDX can be predicted.</span></em></span></em></p>

Testing the Random Walk Hypothesis for Real Exchange Rates

This chapter aims to analyze the efficiency, in its weak form, in the exchange rates of Brazil vs. USA, Australia, Canada, Europe (Euro Zone), Switzerland, United Kingdom, and Japan from July 1, 2019 to September 20, 2020. The results suggest that exchange rates show signs of (in)efficiency, in their weak form (i.e., the values of the variance ratios are lower than the unit), which implies that returns are autocorrelated over time, and there is reversal to the average. In corroboration, the results of detrended fluctuation analysis (DFA) show persistence in yields (i.e., the existence of long memories), thus validating the results of the Lo and Mackinlay model that show autocorrelation between the series of yields. As a conclusion, the authors show that the assumption of market efficiency may be questioned, since the forecast of market movement may be improved if the lagged movements of the other markets are taken into account, allowing the occurrence of arbitrage operations in these foreign exchange markets.

The Relationship Between Gold and Stock Markets During the COVID-19 Pandemic

This chapter aims to analyze portfolio diversification in the US, Europe, UK, Hong Kong, China, Japan, and the gold market (XAU) from January 2019 to July 2020. The results indicate that the markets have very significant causalities, which may call into question efficient portfolio diversification strategies. The DFA exponent coefficients suggest that the random walk hypothesis is rejected in certain markets, which has implications for investors, since some returns can be expected, creating opportunities for arbitrage and abnormal profits. These findings also open space for market regulators to take action to ensure better information among international financial markets. In conclusion, the authors believe investors should diversify their portfolios and invest in less risky markets in order to mitigate risk and improve portfolio efficiency.

MARKET EFFICIENCY IN ITS WEAK FORM: THE PRE-COVID AND COVID INDONESIA ANALYSIS

This essay aims to analyze the efficiency, in its weak form, in the Exchange Markets IDR/MYR (Indonesia-Malaysia), IDR/PHP (Indonesia-Philippines), IDR/SGD (Indonesia-Singapore), IDR/THB (Indonesia-Thailand), IDR/GBP (Indonesia-UK), IDR/US (Indonesia-USA), IDR/EUR (Indonesia-Euro Zone/Europe). The sample comprises the period from September 3, 2018, to October 20, 2020, and the sample was partitioned into two subperiods: Pre-Covid and Covid. To carry out this analysis, different approaches were undertaken to assess whether: (i) the global pandemic promoted in(efficiency) in the exchange rates of Indonesia vs Malaysia, Philippines, Singapore, Thailand, UK, USA, Eurozone? The results suggest that in the Pre-Covid subperiod we can see that the random walk hypothesis is rejected, IDR/MYR (0.61), IDR/SGD (0.60), IDR/US (0.59), IDR/THB (0.56), IDR/EUR (0.55), IDR/GBP (0.54), except for the IDR/PHP pair (0.45) which evidences anti persistence. Already in the Covid period, we noticed that persistence increased significantly, like followed, IDR/EUR (0.82), IDR/PHP (0.81) IDR/SGD (0.80), IDR/US (0.80), IDR/MYR (0.78), IDR/THB (0.71), IDR/GBP (0.62). These findings show high levels of arbitrage, i.e., investors will be able to obtain abnormal profitability without incurring the additional risk, which could jeopardize the implementation of efficient portfolio diversification strategies due to market imbalance. The authors believe that these findings can help policymakers formulate a comprehensive response to improve the efficiency of the foreign exchange market during a global pandemic event.

Examining the random walk hypothesis in the Amman stock exchange: An analytical study

The current study aimed to examine the weak-form efficiency of the Amman Stock Exchange using the weekly stock closing prices of shares for the period 2017-2019. In order to achieve the research objective, the study used the time lags that occurred between one and three weeks through the following tests: simple regression, Pearson correlation coefficient, and Spearman correlation coefficient. The study sample consisted of 179 companies. The current study concluded that the weekly stock closing prices of the shares of public joint-stock companies in the Amman Stock Exchange do not follow the Random Walk Hypothesis of prices, and therefore, do not follow the characteristics of a normal distribution. Therefore, the Amman Stock Exchange is inefficient at the weak-form level. Consequently, the lack of randomness in weekly stock closing price movements does not comply with the hypothesis of the first study. Likewise, the lack of independence of the changes in the current weekly stock closing prices from the previous ones also does not correspond to the hypothesis of the second study.