This means the SAMPLE MEAN or average. You need to add all numbers in the sample
and divide by the number of observations. So, for example if you have 5 numbers
2, 3, -2, 0, 8
then the sample mean is
^{(2 + 3 - 2 + 0 + 8)}/_{5} = 2.2
Sample mean is the most common
statistics that we use to measure * central tendency *.
Andrei