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Measures of Spread – Interpreting Standard Deviation

Standard deviation of data gives a lot of information about data that is approximately bell-shaped. Adrian Gepp explains more in this video.

Interpreting Standard Deviation

Standard deviation is an important measure of spread because of how it can be interpreted for data that is approximately bell-shaped. Specifically, it gives an indication of how much is how far away from the mean. If the data is approximately bell shaped then:

  • 68% of the data is within plus or minus one standard deviation around the mean
  • 95% of the data is within plus or minus two standard deviations around the mean
  • 99.7% of the data is within plus or minus three standard deviations around the mean

This result means that standard deviation is a very descriptive statistic! Now that we have some tools for measuring spread, let’s look at how we measure shape in the next step.

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