How do I calculate and interpret a z-score?

1 Answer
Jun 7, 2015

A z-score indicates how many standard deviations a data point is from the mean. It is calculated with the following formula:

#z = (X - μ) / σ#, where #X# is the value of tha data point, #μ# is the mean, and # σ# is the standard deviation.
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).