We investigate how transaction costs change the number of characteristics that are jointly significant for an investor's optimal portfolio, and hence, how they change the dimension of the cross section of stock returns. We find that transaction costs increase the number of significant...

Identifying outperforming mutual funds ex-ante is a notoriously difficult task. We use machine learning to exploit fund characteristics and construct portfolios of equity funds that earn positive and significant out-of-sample alpha net of all costs. In contrast, alphas of portfolios selected...