Cash Flow Discounting Leads to “Astronomically” Large Mistakes Over the Long Term
Your humble blogger is a vocal opponent of placing undue faith in single metrics and methodologies, like placing a lot of weight in total cholesterol as a measure of heart disease risk. One of the most troubling examples is the totemic status of discounted cash flow based analyses. It’s a weird defect of human wiring that reducing a story about the future to a spreadsheet and then discounting the resulting cash flows (which means you are now layering a second story, about what you think reasonable investment returns will be over that time period) is treated as having a solidity and weight that simply is not there, a reality of its own that manages to take precedence over the murky future it is meant to help understand.
An article by physicist Marc Buchanan in Bloomberg gives a layperson’s summary of an important paper by Yale economist John Geanakoplos, and Doyne Farmer, a physicist at the Santa Fe Institute. It shows that the conventional use of discounted cash flow models over long time periods, as is often the case when discussing environmental impacts, is fatally flawed.
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