  Stock markets can be characterized by fat tails in the volatility
distribution, clustering of volatilities and slow decay of their time
correlations. For an explanation models with several mechanisms and
consequently many parameters as the Lux-Marchesi model have been used. We show
that a simple herding model with only four parameters leads to a quantitative
description of the data. As a new type of data we describe the volatility
cluster by the waiting time distribution, which can be used successfully to
distinguish between different models.
