Standard Deviation

Standard deviation measures how far results spread from the average value.

Standard deviation is a statistical measurement of the amount a number varies from the average number in a series.

• A low standard deviation means that the data is very closely related to the average, thus very reliable.
• A high standard deviation means that there is a large variance between the data and the statistical average, and is not as reliable.

¹

For a normally distributed curve²,

• ~68% of the data falls within 1 SD of the mean (i..e, $\mu \pm \sigma$)
• ~95% of the data falls within 2 SD of the mean (i..e, $\mu \pm 2\sigma$)
• ~99.7% of the data falls within 3 SD of the mean (i..e, $\mu \pm 3\sigma$)

Footnotes

1. https://www.yourdictionary.com/articles/standard-deviation-examples ↩

2. https://www.businessinsider.com/standard-deviation-2014-12 ↩