An article that I found worthwhile which may be of interest to some and I haven't seen picked up broadly yet comes from UCLA Anderson and is entitled "Single-Family Rental Returns: What Drives Investor Return?" The authors find that prior research has only considered either net yield or price appreciation, to the exclusion of the other, so they looked at both. They find a total average return of 9% for the period they looked at (1986 to 2014), and conclude:
"Each component contributes approximately equally to the aggregate U.S. portfolio of housing returns, so excluding one component excludes half of total returns on average,"
There is also a helpful graph comparing the breakdown between the two factors in the 30 largest metro areas.