A z-score is a numerical value that depicts how many standard deviations one is from the mean. A z-score is measurement in terms of standard deviations. A z-score can range from negative values to positive values. A z-score of zero represents a score identical to the mean. If the z-score is negative the value lies below the mean and a positive z-score represents a value greater than the mean. Z-scores can be used to standardise values so comparisons can be made. Calculating a z-score is simple and fast. It requires three pieces of information. Once calculated a z-score has many uses. Commonly two z-scores can be compared to make interpretations about one’s knowledge.