<prompt>  Human: I have a 401K that is roughly the same size as my Vanguard account. Both accounts have about a 5050 stockbond split, too.It occurred to me that one type of account may be better for one type of investment, but which one? Ive read entire books about portfolio allocation, but they often just casually remark that its better to keep bonds in the 401k, with no further explanation. Ive also read in an older book, possibly unaware of low interest rates that it doesnt matter.Is there any research on that topic at all, or am I just missing something that is obvious to everyone else? 