Irrationally high discount rates

I believe, without being able to point to any particular study as evidence, that it is common wisdom in economics and sociology that humans have very high discount rates. That is to say, given the choice between a chocolate now, or two in a year, we’re quite likely to take the instant gratification, even though that’s a 100% interest rate. And, conversely, given the 3-4% interest rates we can get on savings, we don’t save anywhere near enough to support ourselves in old age; and we weight the instant pleasure of the cigarette higher than the 50% chance of premature death, and so on.

I’ve argued before that discounting rates are a measure of probability. It is quite reasonable for me to be indifferent between a chocolate now, or two in a year, if I estimate my chances of dying in that year to be 50%. The expected payoff is 1 chocolate either way. Now, few people make this kind of calculation explicitly; most rely on gut feel. And it seems to me that the gut feel may have been programmed by an environment rather deadlier than that of your average suburbanite. If Ug the Caveman has a 10% chance of not seeing his next Christmas, it’s quite sensible for him to demand a 10% interest rate on his deposits at his local bank. (Modulo how much he cares about his heirs, of course.) But if John the Suburbanite, still using Ug’s heuristic, has the same underlying estimate of his survival probability, he’s making a mistake.


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