Stanford University professor of finance Darrell Duffie, who was interviewed by Businessweek, acknowledged the explosive growth of ETFs, which grew from only 80 funds in 2000 to more than 1,400 in 2013. Actively managed funds, which charge a fee to manage investment portfolios, may decline in popularity, as ETFs become more prevalent. Many mutual funds will also launch their own ETFs to capture more of the market share for mutual funds that they would otherwise lose to new, cheaper, passively managed products.