You get what you pay for: Guaranteed returns in retirement saving accounts (William G. Gale, David C. John, Bryan Kim, Brookings)

The sharp downturn in the value of financial assets between 2007 and 2009 serves as a pointed example of how risky assets can quickly lose significant value. This experience, coupled with continuing concerns about retirement security, has generated new interest in the idea of having the government provide minimum rate-of-return guarantees for retirement savings accounts.

http://www.brookings.edu/research/papers/2016/03/14-guaranteed-returns-in-retirement-saving-accounts-gale