Jarwulf Posted November 5, 2012 Share Posted November 5, 2012 hi, i need to know on intuitive terms why roughly 68% of a randomly sampled population falls within 1 standard deviation of the mean and 95% within 2 sd etc. There doesn't seem to be any explanations on the web besides blurting out CLT or some hocus pocus with arcane calculus symbols. Thanks Link to comment Share on other sites More sharing options...
CaptainPanic Posted November 5, 2012 Share Posted November 5, 2012 Isn't the standard deviation just a definition? It's like asking why a meter is exactly 100 centimeters? It's because we defined it to be like that. Link to comment Share on other sites More sharing options...
imatfaal Posted November 5, 2012 Share Posted November 5, 2012 The wikipage on the 68-95-99.7 rule says the following In statistics, the 68-95-99.7 rule — or three-sigma rule, or empirical rule — states that for a normal distribution, nearly all values lie within 3 standard deviations of the mean. Note the third name - the empirical rule. The Standard deviation is a defined calculation, and the normal distribution just is; there is no ulterior motive or design - just a very useful consequence Link to comment Share on other sites More sharing options...
ewmon Posted November 5, 2012 Share Posted November 5, 2012 There's the Central limit theorem and Central tendency. Link to comment Share on other sites More sharing options...
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