Evaluation Of The Nigerian Stock Market Efficiency In The Pre And Post Financial Meltdown

The controversy surrounding the interaction between efficient stock market hypothesis and financial crisis suggests mixed results for the Nigerian stock market efficiency prior to the financial crisis. The study evaluated the Nigerian stock market efficiency in the pre and post financial meltdown. The objectives were to: (i) examine the efficiency form exhibited by the market before and after the meltdown; (ii) determine the risk-return relationship before and after the meltdown; (iii) examine the magnitude of volatility persistence before and after the meltdown; and (iv) investigate the impact of good or bad news on return volatility in the Nigerian stock market before and after the meltdown.rnrnThe study employed ex-post facto research design and covers the Nigerian Stock Exchange (NSE). Secondary data obtained from the NSE were the weekly All Share Index structured into (January 2001-March 2008) pre, (April 2009-December 2016) post financial meltdown, while March 2008 till April 2009 is the meltdown event window. The data, based on market efficiency hypothesis, were subjected to variants of Generalised Auto-Regressive Conditional Heteroscedasticity models which capture heteroscedasticity and volatility clustering in the error term under Gausian, Student’t and Generalised error distributional assumptions. rnrnThe findings of the study were that:rn(i) previous week return residual (α_i) pre = 0.275426, 0.362653, 0.311980; post = 0.263188, 0.251813, 0.251136 and previous week return variance (β_j) pre = 0.040516, 0.206215, 0.170131; post = 0.651247, 0.656755, 0.655032; p < 0.05, indicates that theNSE is significantly inefficient in the weak form during pre and post meltdown while the market is efficient in the semi strong form after the meltdown;rn(ii) the risk-return relationship is insignificantly negative during the pre and post meltdown with standard deviation (σ) pre = -0.919469, -0.294432, -0.252137; post = -0.120140, rn -0.032694, -0.111328; p> 0.05;rn(iii) the magnitude of volatility persistence is low (β_j+α_i = 0.315942, 0.568868, 0.482111) and dying very fast (ln⁡(0.5)/ln(α+β) = 0.601588, 1.228752, 0.950062) before the meltdown while volatility persistence is high (β_j+α_i = 0.914435, 0.908568, 0.906168) and dying very slowly (ln⁡(0.5)/ln(α+β) = 7.749086, 7.228902, 7.034845) after the meltdown. The return series revert to its mean in 1 and 7 weeks before and after the meltdown respectively; andrn(iv) the return volatility responded more to positive (good) news than negative (bad) news of the same magnitude before the meltdown (γ_i = 0.222173, -0.583358, -0.616583; p < 0.05) butinsignificantly responds more to negative (bad) news than positive (good) news of the same magnitude after the meltdown (γ_i = -0.033144, 0.078015, 0.047045; p > 0.05).rnrnThe study concluded that information is irregular, not opened and unbalanced, leading to information asymmetry and the information environment of the NSE is unconducive and unattractive for shrewd investors. Therefore, the study recommended free flow of relevant securities information through the development and provision of latest and user friendly software application for stock information dissemination. Provision of on-line real time access to share price movement will enable investors make informed decision and also reduce insider trading in the market.

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