Our discussion steps from the simple asset market model studied in Berg et al.
(2001), which describes a population of heterogeneous individuals, who receive a
private signal on the dividend of a given asset. Given their private signal, agents
invest in the asset and their demand determines the price, via market clearing.
Agents learn how to optimally exploit their private information in their trading
activity, which has the effect that their information is incorporated into prices.
As the number N of agents with a different private information increases, prices
gradually converge to the dividends. Beyond a critical number of agents, prices
converge exactly to dividends. Therefore, the model provides a stylized picture
of how markets aggregate information into prices and become informationally
efficient.
In this setting, we introduce non-informed agents who adopt the same learning
dynamics, but which base their decision on public information, rather than on a
private signal. In particular, we take the sign of the last return as public signal,
which mimics a chartist behavior, in its simplest form. Our main result is that
chartists take over a sizable share of market activity only when the market becomes
informationally efficient.
The rest of the paper is organized as follows. The next section introduces the
model and the notation. In the following section we first recall the results with only
informed traders and then discuss the effect of introducing non-informed traders.
The paper concludes with a discussion of the extension and relevance of the results.
2 The Model: Information Efficiency and Chartists
Let us consider a market where a single risky asset is being traded an infinite
number of periods. There is also a risk-less asset with an unitary price and which
pays one at the end of each period. This is equivalent to considering, for the sake
of simplicity, discounted prices right from the beginning. Let there be N types of
informed traders (fundamentalists) and one type of uninformed traders (chartists)
operating in the market. For simplicity, we assume that all uninformed traders are
on the same type, i.e. adopt the same trading strategy. The description of chartists
can then be given in terms of a single representative agent, which will be referred
as agent i = 0. Similarly, all fundamentalists of the same type, i.e. having the same