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