Review of basic probability and statistics Probability: basic deﬁnitions • A random variable is the outcome of a natural process that can not be predicted with certainty. – Examples: the maximum temperature next Tuesday in Chicago, the price of Wal-Mart stock two days from now, the result of ﬂipping a coin, the response of a The answer is that in "Intro to Statistics" classes, they give a rule of thumb that, for "nice" distributions, n = 30 is large enough that claiming the sample mean is approximately normally distributed is probably not that far off the truth if you know the population standard deviation, and this is justified because of the asymptotic behavior ...

*Sensibly organized for quick reference, Statistical Rules of Thumb, Second Edition compiles simple rules that are widely applicable, robust, and elegant, and each captures key statistical concepts. This unique guide to the use of statistics for designing, conducting, and analyzing research studies illustrates real-world statistical applications ...*A simple ShortTutorial on How to Find Standard Deviation Using thumb Rule with a brief explanation of formula and example. How to Find Standard Deviation of Thumb Rule Rule of thumb is a method of procedure or principle that is based on the experience and practical application but not the theory or scientific results. Rule of thumb definition is - a method of procedure based on experience and common sense. a method of procedure based on experience and common sense… See the full definition