**1. Introduction**

The practice of short selling and profiting from a fall in share price has been around for at least four centuries. In 1609, Isaac Le Maire formed a secret company to short shares in the East India Company in anticipation of a new French firm that would offer stiff competition (Bris et al. 2007). As events played out, the creation of the French rival never occurred, and the ensuing litigation provided ye<sup>t</sup> another argumen<sup>t</sup> to ban short selling practices in the marketplace.

Potential abuse has led regulators to ban short selling in a number of national exchanges. Restrictions on short selling are especially commonplace in emerging markets, and exist because of an outright ban or lack of institutional mechanisms to borrow stock.<sup>1</sup> Moreover, in many of these markets there are no parallel option markets to effect a short sale through the buying of puts or writing of calls. As short selling restrictions inhibit information flow, market prices may be slow to adjust to news.

While potential abuse has led to a ban on short selling in a number of exchanges, a strain of research suggests that short sale restrictions may inhibit the price discovery process. For example, Miller (1977) argues that with divergence of opinion, a short sales ban results in the overvaluation of a security. Diamond and Verrecchia (1987) develop a formal model to discuss the importance of short selling in the asset price adjustment process. They show that constraints do not bias prices upward, although they do reduce the adjustment speed of prices to private information.

One way to test for the effect of a short selling ban is to investigate any differences in price discovery across regime shifts. For example, Beber and Pagano (2013) examine how temporary bans

<sup>1</sup> For a list of global short selling regulations, see Jain et al. (2013).

in short selling around the world following the financial crisis of 2007–2009 led to a deterioration in market liquidity.

This was especially true for stocks with small market capitalization and no listed options.<sup>2</sup> They displayed slower price discovery, especially in bear markets.<sup>3</sup>

A short selling ban may hinder price discovery even when news is positive. This can occur if investors overreact to information, leading to a reversal of prices (see, De Bondt and Thaler 1985). Atkins and Dyl (1990) first find evidence of market overreaction using daily returns. To the extent that market corrections require a decrease in returns, a ban on short sales may further inhibit the price discovery process.

In the following analysis, we examine the effect of short sale restrictions on market efficiency for the Dhaka Stock Exchange (DSE). The DSE has always had a ban on short selling of securities, so performing any type of test that depends upon a regime change is not possible. Instead, we rely on a battery of runs tests to examine market efficiency and the ability of prices to adjust rapidly to new information. In particular, we test for statistical independence, and employ a standard non- parametric runs test that looks at clusters of price changes in the same direction.

To further test for the effect of short selling restrictions, we also consider the distribution of daily price runs. Any evidence of an asymmetric distribution with an unusual number of long, negative return runs would sugges<sup>t</sup> that a ban on short selling inhibits rapid price adjustment to adverse information. On the other hand, if investors overreact to positive news, a short sale ban may delay any market correction. In this situation, the distribution of daily price runs would display an unusual number of longer runs with positive price changes.

Previous work on the Dhaka Stock Exchange provides conflicting evidence regarding market efficiency on the Dhaka Stock Exchange. Islam and Khaled (2005) consider DSE index returns for the period 1990–2001. They sugges<sup>t</sup> that structural changes put in place after the market crash of 1996 led to market efficiency. Their statistical tests show short term predictability of share prices prior to the crash, but not subsequently.

Mollik and Bepari (2009) use the runs test to investigate the weak form market efficiency of the DSE. They examine two stock indices from 2002–2007 to see whether there was an unusual number of runs. In contrast to Islam and Khaled (2005), they find that returns do not follow a random walk, and reject weak form efficiency of the DSE in the post-crash period.

In addition to DSE index returns, Mobarek et al. (2008) examine individual stock returns from 1988–2000 provided by a data vendor. Even allowing for structural changes following the 1996 crash, they find that there is significant auto correlation over the sample period. They reject weak form market efficiency and call for additional studies using market price information.

Our analysis updates the sample time period, and following the suggestion of Mobarek et al. (2008), examines the dynamics of individual stock price data obtained directly from the exchange. This allows us to also adjust for dividends, share splits, and other corporate events. Additionally, we introduce runs tests that specifically investigate for the effect of short sale restrictions on price adjustment; for robustness, we compare our results to evidence from the U.S. and Australian stock markets.

The runs test analysis suggests that DSE stock returns are not independent. Moreover, DSE stock prices appear to incorporate information more slowly than one would expect, with the daily runs

<sup>2</sup> Swidler (1988) provides one early empirical study of the effect of short shale restrictions on stock prices and the further effect when there is option trading. He shows that with heterogeneous expectations, estimation risk is more important than short selling restrictions in explaining asset returns. Moreover, for stocks with listed options, investors can synthetically sell short via long puts or short calls. The evidence finds that for stocks with listed options, only estimation risk is important in determining asset returns.

<sup>3</sup> Still another study that looks across regime changes is Wang (2014). He finds that when Chinese regulators lifted the short selling ban on 90 stocks in 2010, they experienced a significant price decline. Moreover, the price declines were positively related to the amount of short selling and is consistent with the notion that short selling can be used as a mechanism to correct for overvaluation.

distributions exhibiting fatter tails for DSE stocks than for US stocks. In other words, for both good and bad news, the DSE ban on short selling causes prices to adjust more slowly to a new equilibrium, resulting in a disproportionate number of lengthy return runs. For emerging market exchanges that have never experienced short selling, this novel application of the runs test provides a valuable tool to analyze the effect of short sale restrictions on asset price dynamics.
