Weak-Form Market Efficiency, Estimation Interval and the Nigerian Stock Exchange: Empirical Evidence
Abstract: Given the desirability of efficient capital markets in aiding optimal resource mobilization and allocation in the financial system, this paper is an attempt to investigate the efficiency level of the Nigerian Stock Exchange (NSE) across different data estimation intervals with reference to the weak-form variant of the Efficient Market Hypothesis (EMH). The paper employed daily, weekly, monthly and quarterly aggregate stock price data using the NSE All Share Index series from 4th January, 1999 to 3P1 December, 2013 to test for the weak-form efficiency of the NSE using a combination of seven (7) statistical and parametric tools namely- Autocorrelation tests, the ADF and P-P unit root tests, Variance Ratio tests, the Normality/Random Walk tests, the Granger Causality test, the ARCH-GARCH test and Regression rest. The empirical results of the investigation indicate that on balance the NSE is weakjorm inefficient when daily, weekly, monthly and quarterly prices are examined irrespective of the estimation interval and the parametric test employed in the tests. It is to be noted from the findings that the NSE is still weak-form inefficient despite the implementation of various capital market reforms undertaken in the recent past as well as the adoption of automation and JCT in the operations of the Exchange. It is therefore recommended that these salutary reforms and policies should be intensified and sustained to ensure efficiency of the NSE.
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Authors: Onyemachi Maxwell Ogbulu
