Employers beware: changing your retirement plan’s design can have unfortunate, unintended consequences for your employees. That’s what happened to the Thrift Savings Plan (TSP) for federal workers, says a new study by a team of researchers for the NBER Retirement and Disability Research Center. Like many private-sector savings plans, the $500 billion TSP – one of the nation’s largest retirement plans – has automatic enrollment. Federal employees can make their own decision about how much they want to save and, in a separate decision, how to invest their money. But if they don’t do anything, their employer will automatically do it for them. In 2015, the TSP changed its automatic, or default, investment from a government securities fund to a…