Yes, a data value is typically considered an outlier if its z-score falls below -2 or exceeds 2. The z-score is a statistical measurement that describes a value’s relation to the mean of a group of values. Specifically, it indicates how many standard deviations a data point is from the mean.
A z-score less than -2 means that the value is more than two standard deviations below the mean, while a z-score greater than 2 indicates that the value is more than two standard deviations above the mean. In a normal distribution, these extreme z-scores suggest that the data point is unusual compared to the rest of the data set. This is why such values are often classified as outliers, signaling that they could be due to variability in the measurement or might indicate a more significant issue that needs to be investigated.