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The Standard Deviation and Coefficient of Variation
Home What is Statistics? A Population and Sample A Parameter and a Statistic Quantitative and Categorical Data Discrete and Continuous Nominal, Ordinal, Interval and Ratio Describing the Center of Data Describing the Variability of Data The Standard Deviation and Coefficient of Variation The Empirical Rule Percentiles and The Five-Number SummaryView All Tutorials
 Percentiles and The Five-Number Summary
Fundamentals of Statistics 1: Basic Concepts :: The Empirical Rule
The standard deviation is the way variability is often described. If the data we are working with are roughly bell-shaped and symmetrical (looking like a normal distribution) then we can use the standard deviation to tell approximately how much of the data will cluster around the mean.



The so called empirical rule states that the bulk of the data cluster around the mean in a normal distribution. In fact:
  • 68% of values fall within ±1 standard deviation of the mean
  • 95% fall within ± 2 standard deviations of the mean
  • 99% fall within  ± 3 standard deviations of the mean
It's called the empirical rule since experimenters have observed roughly these patterns from their data over and over again when they empirically collect data.

 
The Standard Deviation and Coefficient of Variation
Home What is Statistics? A Population and Sample A Parameter and a Statistic Quantitative and Categorical Data Discrete and Continuous Nominal, Ordinal, Interval and Ratio Describing the Center of Data Describing the Variability of Data The Standard Deviation and Coefficient of Variation The Empirical Rule Percentiles and The Five-Number SummaryView All Tutorials
 Percentiles and The Five-Number Summary

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March 14, 2021 | Abbi Popo wrote:
I need to read it over and over again.
 
December 4, 2017 | joyce wrote:
thanks
 
December 4, 2017 | joyce wrote:
thanks
 
April 22, 2015 | Nita Wright wrote:
The empirical rule is confusing to me in a way because it is discussing the date we've collected and how it can be off by 1-3 plus or minus. It might seem silly but while understand where the variation comes from I find it disconcerting at the same time. I feel like data can change from the group we are working with but the results from those groups wouldn't necessarily change. Does that make any sense?
 
November 16, 2012 | kenya wrote:
I love this website am so going to do well i my stats exam