In statistics, the standard score is the number of standard deviations an observation or datum is above the mean. Thus, a positive standard score represents a datum above the mean, while a negative standard score represents a datum below the mean.  Standard scores are also called z-values, z-scores, normal scores, and standardized variables; the use of "Z" is because the normal distribution is also known as the "Z distribution".  Based on an individual Age, weight, height and other indices Z-Score can be calculated to check if the growth of the individual is normal.