Dynamics of the number of trades of financial securities

We perform a parallel analysis of the spectral density of (i) the logarithm of price and (ii) the daily number of trades of a set of stocks traded in the New York Stock Exchange. The stocks are selected to be representative o f a wide range of stock capitalization, The observed spectral densities sho w a different power-law behavior. We confirm the 1/f(2) behavior for the sp ectral density of the logarithm of stock price, whereas we detect a 1/f-lik e behavior for the spectral density of the daily number of trades. (C) 2000 Elsevier Science B.V. All rights reserved.