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 of a wide range of stock capitalization. The observed spectral densities show a different power-law behavior. We confirm the 1/f2 behavior for the spectral density of the logarithm of stock price, whereas we detect a 1/f-like behavior for the spectral density of the daily number of trades.