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Calculate z-scores (standard scores) to see how many standard deviations a value is from the mean.
A z-score tells you how many standard deviations a value is from the mean. A z-score of +2 means the value is 2 standard deviations above average, while -1.5 means 1.5 standard deviations below.
It depends on context. For test scores, positive z-scores are typically better. About 68% of values have z-scores between -1 and +1, so values outside ±2 are unusual.