Z-Score is one of the linearly derived scores (standard score), with a mean of zero and standard deviation of 1. it shows the difference (or distance) between the mean (of a given group) and any specified raw score value. This is the basic standard score fro which the other standard scores, viz., T-score, CEEB-score, AGCT-score, etc., are derived. Z-score is obtained by subtracting the mean from the raw score and dividing the difference by the standard deviation. Hence, the value of Z-score may be either positive or negative and ranges from -3 to +3. the formula to obtain Z-score is,
Z = x - x##
s.d.Where, x = any raw score.
x## = mean of the set of raw scores.
s.d. = standard deviation