standaard deviatie

Range Rule of Thumb

Interpreting a Known Value of the Standard Deviation If the standard deviation of a collection of data is a known value, use it to find rough estimates of the minimum and maximum usual sample values as follows:

minimum “usual” value = (mean) — 2 X (standard deviation)
maximum “usual” value = (mean) + 2 X (standard deviation)

Estimating a Value of the Standard Deviation s To roughly estimate the standard deviation from a collection of known sample data, use

s === range/4

where range = (maximum data value) — (minimum data value).



Empirical Rule


A concept helpful in interpreting the value of a standard deviation is the empirical rule. This rule states that_/or data sets having a distribution that is approximately bellshaped, the following properties apply. (See Figure 3-3 on the next page.)
  • About 68% of all values fall within 1 standard deviation of the mean.
  • About 95% of all values fall within 2 standard deviations of the mean.
  • About 99.7% of all values fall within 3 standard deviations of the mean.

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