Before revision:  In this respect, important variables are the trading activity, defined here as the number of trades N, and traded volume V in the asset , its price P, the squared volatility \sigma^2, the corresponding bid-ask spread S and the cost of trading C. Different reasonings result in simple proportionality relations ("scaling laws") between these variables.
After revision:  In this respect, important variables are the trading activity, defined here as the number of trades N, and traded volume V in the asset , its price P, the squared volatility \sigma^2, the bid-ask spread S and the cost of trading C. Different reasonings result in simple proportionality relations ("scaling laws") between these variables.