z-score: A measure of how much standard deviation about the mean, z
 

              The z-score, z, for a particular, x, is
 

    Example:
            from a list of data we find the mean = 30, the standard deviation = 10;
            how much is 45 relative to rest of data?

                    z-score = (45 - 30 ) / 10 =- 1.5 or 1.5 standard deviation above the mean

                    From the z-score normal distribution table:
                    means 45 greater than about 93.5 % of data

            Compare 20 relative to rest of data:
 
                    z-score   (20 - 30 ) / 10 = -1 or 1 standard deviation below the mean
 

                        From the z-score normal distribution table:
                    means 20 greater than about 15.5 % of data