This was covered in the article: Vanguard has invested heavily in technology. Algorithms help managers figure out where to buy and sell while minimizing market

This was covered in the article: Vanguard has invested heavily in technology. Algorithms help managers figure out where to buy and sell while minimizing market impact. Risk software makes sure the portfolio stays close to the index. Because of these technologies, Brennan says, “we probably have the most assets per head of any asset manager in the world.” (The key determinant of staffing, he says, is the number of portfolios, not the assets in them.) But you can automate only so much, and the tough decisions still fall to the portfolio managers. When is the best time to buy an illiquid stock that trades only once or twice a day? How do you handle a corporate deal structured in an unusual way or the issuing of a new class of stock? “People think a computer could run index funds­—and they’re so wrong,” says Brian Bruce, a former index fund manager who’s now chief executive officer of Hillcrest Asset Management in Plano, Texas, and editor-in-chief of the Journal of Index Investing.