One key challenge for the short selling literature is to identify the incremental contribution
of various measures of short sale constraints. Although variables such as loan fee,
loan supply and short interest are determined simultaneously in the market for borrowing
stock, new incremental information may be found in each variable examined. Papers such
as Beneish et al. (2015) attempt to disentangle the effect of one particular variable, and
attempt to shed light on the parallel challenge faced by investors in determining which
variables will make the most impact on returns as well as trading costs. We discuss a
number of practical approaches to this challenge, and we also consider a potentially new
take that considers accounting-data-driven anomalies as one of the possible exogenously
determined variables in the equilibrium of the equity loan market.
1. Introduction
This article will address some of the key challenges in conducting empirical research in the area of short selling. Specifically,
we will address the following: (1) the endogeneity problem with respect to the connection among short interest,
fees, and supply, and the associated difficulty in disentangling incremental results; (2) how the extant literature has
addressed this endogeneity problem, to the extent that it has; and (3) a fresh approach: viewing short selling as a metaanomaly
and asking what is truly exogenous.
Beneish et al. (2015, BNL hereafter) study the determinants and consequences of the level of lendable supply. The authors
find that lendable supply "is sensitive to borrowing costs and to firm characteristics." They write, "Controlling for the
holdings and investing preferences of institutions, we find that shares are often least available to borrow when they are
most attractive to short sellers." Furthermore, the authors find that "supply is a key feature distinguishing constrained from
unconstrained stocks, and that, among constrained stocks, those with the lowest supply have the strongest negative
returns."
Overall, BNL find that limits to the supply of lendable shares is a key impediment to pricing efficiency in capital markets.
One key premise in BNL is that supply should be considered as a fresh element in our set of observations of short selling
constraints. However, this article will argue that the supply of available shares is closely related to other variables: demand
for borrowing, price for borrowing, quantity borrowed, and short interest. Of course, we might glean valuable, and truly
new, insights by studying a database that shows the incremental effect of supply. However, supply should not be considered
as a completely independent view of the equilibrium relationship among quantity, price, and demand.