  Presented is an analytic microeconomic model of the temporal price dispersion
of homogeneous goods in polypoly markets. This new approach is based on the
idea that the price dispersion has its origin in the dynamics of the purchase
process. The price dispersion is determined by the chance that demanded and
supplied product units meet in a given price interval. It can be characterized
by a fat-tailed Laplace distribution for short and by a lognormal distribution
for long time horizons. Taking random temporal variations of demanded and
supplied units into account both the mean price and also the standard deviation
of the price dispersion are governed by a lognormal distribution. A comparison
with empirical investigations confirms the model statements.
