The z-score is the number of a data value that represents how many standard deviation is it from the mean. It is calculated from the ratio of the difference of a data value and the population mean and the standard deviation of the data set. Having a z-score of zero would mean that the value is the same as the mean. A z-score that is greater than 1 would mean that the value is x standard deviation greater than the mean. If for a certain data, a z-score of positive 2.5 is calculated, then it means that the data is 2.5 standard deviations away and above from the mean of the whole set. In a normal
