add visual estimation of standard deviation to tutorial chapter 2

ScPoEcon / ScPoEconometrics

Undergraduate textbook for Econometrics with R

https://ScPoEcon.github.io/ScPoEconometrics/

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Closed floswald closed 5 years ago

floswald commented 5 years ago

if x is approx normally distributed, 95% of all data fall within 2 std devs +/-.
that is, 4 std devs cover 95% of data
that is, a rough estimate of the std dev of a variable is to do range(x) / 4.