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A Z is a statistical measurement that usually shows the relationship of a score to the mean in a group of scores put together.A Z-score of 0 means the mean and the score are equally the same.A Z-score can also be negative or positive,this indicates whether it is above or below the mean and by how many standard deviations.besides showing the a score's relationship to the mean, the Z-score gives indications to statisticians whether a score is typical or atypical for a particular set of data .One application in real -life of z-scores occurs in usability testing.
it is used to standadize data on one scale so a comparison can take place
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