All you have to do to see that the Old School SWR studies are in error is to take note of how much the number changes
with changes in valuation levels.
The risk / reward ratio of stock investing VARIES
with changes in valuation levels.
SInce the riskiness of stocks changes
with changes in valuation levels, the important thing is to CHANGE your stock allocation as needed to keep your risk profile roughly constant.
The safe withdrawal rate is not a constant number but VARIES
with changes in the valuation level that applies on the day the retirement begins.
The New School studies say that the SWR varies
with changes in the valuation level that applies on the day the retirement begins.
Not exact matches
It seems like a better way of looking at this issue would be to pick a beginning and end point
with average
valuations (or at least the same
level of
valuation) so that the results aren't biased by a
change in valuation.