The standardized residual equals the value of a residual (ei) divided by an estimate of its standard deviation.
Use the standardized residuals to help you detect outliers. Standardized residuals that are greater than 2 and less than −2 are usually considered large enough to investigate.
Standardized residuals are useful because raw residuals might not be good indicators of outliers. The variance of each raw residual can differ by the x-values associated with it. This unequal scale causes it to be difficult to assess the sizes of the raw residuals. Standardizing the residuals solves this problem by converting the different variances to a common scale.