We in the trade refer to the relationship between rents and sale prices as a factor rather than a percentage.
Instead of:
Rent / Sale Price = %
We normally use:
Sale Price / Rent = Gross Rent Multiplier (which is a factor)
Your apparent point remains the same: between 1950 – 1980 or so the ratio of rents/sale prices increased from about .4% to about .50%. Between 1980 – 2000 or so the trendline itself – which is comprised ot the highs and lows – stayed generally constant at about the .50% range, and only during the bubble did it exceed that.
Your chart also demonstrates why Rich uses the 50-year trendline rather than a 100-year trendline. A (real) new paradigm did crop up after WWII, based on a couple factors.