How do I calculate and interpret a z-score?
A z-score indicates how many standard deviations a data point is from the mean. It is calculated with the following formula:
Besides telling us where a data point lies compared with the rest of the data set in relation to the mean, a z-score also allows comparisons of data points across different normal distributions. (For example, we can compare the scores obtained by a student in two exams whose scores are normally distributed).