The intensity of trading activities can be measured in a number of ways. The most common measure in use is volume, which is simply the number of shares traded during a certain time interval. Given that the liquidity (which shows how easy it is to trade an asset) and therefore the absolute trading activity in each stock is different, the volume expressed in percentage form is a more convenient choice for modeling purposes. This measure is called turnover, which is formally computed from volume, as follows:

Here, x stands for turnover, V for volume, and TSO for the total shares outstanding; the latter indicates the total number of shares available for public trading. The index i indicates the actual stock, and index t indicates the time interval.

As mentioned earlier, there are several stylized facts documented in volume. An obvious one is that volume is non-negative, given that it measures the number of traded shares. This number is zero, if there are no trades at all...