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Learning Statistics with Python

Standard deviationStandard deviation

The next term is standard deviation; this value is similar to the variance because standard deviation is a square root of the variance; hence the formulas will vary for the population and sample.

Sample Variance


Standard deviation is a measure of how data spread out in relation to the mean.

68–95–99.7 rule

In statistics, one standard deviation or sigma plotted above and below the mean value corresponds to 68% of data; two sigmas include 95% and three 99.7.

Example Let's figure it out with the sample of kittens' weights in grams.

Sample Variance

Look at the picture; in this case, we deal with such values:

  • Mean value = 100 grams.
  • Standard deviation (sigma - the sign you can see on the picture) = 20 grams.

So, as we said, the one sigma above and below the mean corresponds to 68% of values. In this case, 68% are the values from mean - standard deviation = 100 - 20 = 80 to mean + standard deviation = 100 + 20 = 120.


You have the data distribution with the mean value of 1500 standard deviation of 100. Match the percent of data with the numerical interval.




Click or drag`n`drop items and fill in the blanks

[1400, 1600]
[1300, 1700]
[1200, 1800]

Section 3.

Chapter 4