Weak - Form Efficiency in Karachi Stock Exchange: Evidence from Random Walk Hypothesis

Abstract

he study is aimed at an empirical examination of the weak-form efficiency in Pakistani stock market within the framework of random walk hypothesis. The concept of weak-form efficiency of stock market initially was developed by Fama (1970), under the efficient market hypothesis (EMH), along with two other, strong and semi-strong forms. An efficient market is defined as where “stock prices fully reflect all available information. The efficiency of capital market is one powerful reason investors are so willing to invest in that market. Presence of even weakest form of efficiency in the stock market implies presence of random walk. The current study is based upon KSE, owing to its huge turnover as compared to the other stock exchanges in Pakistan. This particular study is based upon examining the four indices in the exchange and 43 companies selected on the basis of trading frequency of at least 95% days. The study adopted a triangular approach in methodology by using direct and indirect methods for exploring random walk. Directly random walk is tested by applying traditional tests; serial correlation, runs, Kolgomorov-Simirnov, autoregression, variance ratio and unit root tests and ARMA models. However, indirectly random walk is investigated by the presence of seasonal anomalies, volatility clustering, thin-trading and through non-linearity of return series. The empirical findings of the study conducted suggest that Karachi stock exchange does not exhibit weak-form efficiency and random walk for the majority of its firms and indices over the study period. The results reveal the presence of serial correlation and autocorrelation in the returns series of all indices and in most of the firms in the stock market. Similarly, stationary returns at level and non-stationary at difference also reveal the absence of random walk. Significant ARMA values also depict absence of random walk. Presence of anomalies and volatility clustering is found in majority of the indices and in firms. However, the study does support random walk in few of the selected firms and KSE-30 index and to some extent indication of random walk is found in KMI-30 index. Correspondingly, the absence of seasonal anomalies in KSE-30 and to some degree in KMI-30 index is credited to the free-floating methodology of shares in these indices. Similarly, the non-stationary return series of KSE-30 as depicted by unit root tests and GARCH models also supports the evidence of random walk in the index. Likewise, for variance ratio test and ARMA model the null hypothesis for random walk cannot be rejected for KSE-30 index. It is concluded therefore, that for KSE-30 index the evidence found in the study supports the weak-form efficiency. Hence, it can be said that KSE does not follow random walk with exception to KSE-30 index. Auxiliary research on KSE-30 index is however suggested by using a diversified approach and by analyzing weekly and monthly data for the corroboration of the results presented in the study.