For this type of analysis, people typically refer to a constant maturity bond.  At least insitutional investors.  This relates essentially to rebalancing the bond portfolio.  e.g. if you buy a 10 year bond, in six month, you sell it and buy another 10y bond.  and so on.  And you calculate the return of that strategy: a constant 10y maturity bond.  That's what you would get if you buy a passive etf or mutual fund investing in long term gov bonds.  that also includes roll-down yield.