
Transaction costs and portfolio strategies
Transaction costs are a key consideration for the development of trading strategies; and not just in final profitability checks. Indeed, disregard for trading costs at the design stage leads to excessive reliance on fleeting small-scale characteristics for return predictors. It also skews the conventional efficient frontier of portfolio choice towards risky trading strategies. A realistic implementable efficient frontier would penalize risky strategies for trading costs, which in turn depend on the size of the risky strategy allocation. This is particularly important for portfolios with large assets under management whose rebalancing has a large market impact. For the development of algorithmic trading strategies with machine learning, it can be highly beneficial to integrate transaction costs into the learning process. A recent paper proposes a “portfolio machine learning method” to that end.