Calculate Z-score
A z-score refers to the number of standard deviations each data value is from the mean, with a z-score of zero indicating the exact mean. Z-scores are useful for analyzing numbers in the context of the rest of the field.
Example
A GIS analyst for a nongovernmental organization is analyzing a disease outbreak. Calculate Z-score can be used to determine in which areas the outbreak is concentrated.
Usage notes
Calculate Z-score can be found using the Action button 
under How is it distributed? on the Find Answers tab. The input layer can be a point, a line, or an area layer.
A number field must be chosen as the field to calculate the z-score. The number field will be used in the equation (number-average)/standard_deviation.
Optionally, you can enter mean and standard deviation values. If you don't enter values, the mean and standard deviation will be calculated for you.
Calculate Z-score adds a new number field to the input layer. The field name is automatically populated in the Calculate Z-score pane, but you can change it before running the calculation.