“On an equal-weighted basis, the average mid-cap growth fund returned -1.23% and lagged by 328 basis points in 2015, much higher than the expense ratio incurred,” Rosenbluth said. “This suggests to us that unwarranted stock selections contributed to underperformance.”

Additionally, just 12% of all small-cap growth funds outperformed the S&P SmallCap 600 Index. Funds that track larger companies fared slightly better, with 51% of all large-cap growth funds outperforming the S&P 500 Growth index.

Alternatively, investors may have been better off just replicating the various asset categories and styles through relatively cheap index-based ETFs. For example, the iShares S&P 500 Growth ETF (NYSEArca: IVW) tracks the S&P 500 Growth Index and comes with a 0.18% expense ratio. The iShares S&P Mid-Cap 400 Growth ETF (NYSEArca: IJK) follows the S&P MidCap 400 Growth Index and has a 0.25% expense ratio. The iShares S&P Small-Cap 600 Growth ETF (NYSEArca: IJT) reflects the S&P SmallCap 600 Growth Index and has a 0.25% expense ratio.

“In recent years, investors have been shifting assets out of actively managed U.S. equity mutual funds and into passive index mutual funds and ETFs,” Rosenbluth added. “S&P Global Market Intelligence expects the trend to continue. While there are bright spots in every investment style, the appeal of low-cost alternatives that do not take sector bets is highly compelling in our opinion.”