z test

 We saw before that a zscore can be determined by comparing an actual score’s percentile ranking to a table of zscores, but what if the percentile ranking is not known?
 IOW: If we know a test has a standard deviation of 10 and a mean of 100, what is the zscore for a score of a 103?
 We know that z will be positive because it is above the mean. And, we know it will be greater than zero and less than one based on it falling within one standard deviation.
 To compute a z score using statistics, we take the score minus the mean and divide that number by the standard deviation:
z = x_{i} – x̄
SD
z = (103100)/10
= 3/10
= .3