notes-statsHeuristics

In a Gaussian distribution, the ratio of standard deviation to expected absolute deviation is sqrt(pi/2), which is close to 1.25. In a Student's t distribution, it is pi/2, which is close to 1.6 -- http://papers.ssrn.com/sol3/papers.cfm?abstract_id=970480 (i wonder what the derivation is?)

https://en.wikipedia.org/wiki/Rule_of_succession : if there is a binary event like flipping a coin, and you've observed n of them, and heads came up h times, then the Rule of Succession estimate for the bias of the coin (the probability that it comes up heads) is (h+1/n+2). (this is like a Bayesian prior of 1 virtual head and 1 virtual tail events).

There is a heuristic (what is it's name?!?) that suggests that if you want to estimate how long some situation will persist/endure, guess that you are now about halfway through its lifetime; that is, that it will continue on for about as long as it has lasted up until this point, for a total duration of twice as long as it has been so-