The National Bureau of Economic Research recently studied whether mutual fund families acting as trustees of 401(k) plans display favoritism toward their own funds. The study found that poorly-performing funds are less likely to be removed from, and more likely to be added to, a 401(k) menu if they are affiliated with the plan trustee. It also found no evidence that plan participants undo this affiliation bias through their investment choices. Finally, the paper reports that the subsequent performance of poorly-performing affiliated funds indicates that these trustee decisions are not information driven and are costly to retirement savers. The full study can be accessed here.