Answer: sigma is used for measuring Population Standard Deviation.
Step-by-step explanation:
The lower case Greek letter 'sigma' is denoted by the symbol ( ).
This symbol indicates the Population Standard Deviation of the data. Standard deviation means how much variation or dispersion is there in our data. Squaring of standard deviation gives us Variance which is denoted by the symbol .
Formula for Population Standard deviation ( ) is =
,
where = each value from our list of data
= Population mean of data
N = Number of observations in our data
Standard deviation can never be negative and it is very much sensitive to outliers in our data.