The Investment Company Institute published a "Research Perspective entitled, "The Economics of Providing 401(k) Plans: Services, Fees, and Expenses, 2016," which briefly mentions money market funds, which are a minor player in the massive 401k market. ICI's statistics show that just 3% of $3.0 trillion in 401k plans is held in money funds, which totals approximately $90 billion. ICI writes, "Only 3 percent of 401(k) mutual fund assets were invested in money market funds at yearend 2016. 401(k) participants holding money market funds had an asset-weighted average expense ratio of 0.22 percent in 2016, higher than in 2015. Industrywide, the average expense ratio investors incurred on money market funds also rose in 2016. The increase in money market fund expense ratios in 2016 is largely reflective of a change in the current interest rate environment. Recent Federal Reserve decisions to increase interest rates led to the paring back of expense waivers that money market funds had adopted to ensure that net yields did not fall below zero. This caused the expense ratios of money market funds to rise somewhat." ICI's study shows that 63% of 401k plan assets are held in mutual funds overall, and 10% of this total, or about $300 billion, is held in bond funds.