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Empiracle rule & Chebyshev's rule translated in English

posted Oct 18, 2010, 6:09 PM by Prof Kiernan   [ updated Feb 6, 2014, 6:04 AM ]

Question: "I'm really stuck on the part where I have to 'compare the percent of scores within 1 and 2 standard deviations of the mean to both the Normal Curve and Chebyshev'. I've calculated the percent of scores but now what do I do?"

This is the third time I've been asked this exact question today... so here's a general answer for everyone.


If you have the percentages of your data falling between one and two standard deviations all you have to do is compare your percentages to the percentages in the empiracle rule and Chebyshev's Rule... Basically you need to answer the following question and explain your answer:

Does your data look more like the data from:
  • the empiracle rule (1 standard deviation has about 68% of your data and 2 standard deviations has 95% of your data) 
  • Chebyshev's Rule (75% within two standard deviation and 89% within 3 standard deviations)? 
  • If neither, apply the normal curve (the Z formula) and see if that looks more like your values. 

I hope this helps
-Prof. K.