Research Design and Statistical Consulting

George M. Diekhoff, Ph.D.

Every so often I stumble across another SPSS quirk. Recently I was doing some customized partial and semi-partial correlations that aren’t available through the SPSS menu system, but rather, required that I residualize some variables myself. Using the SPSS Regression procedure, I saved the “standardized residuals” to my data file. Just out of curiosity, and my natural tendency to check everything twice, I calculated the mean and standard deviation of these “standardized residuals.” Not surprisingly, the mean was 0, as it should be. However, the standard deviation was NOT 1.0, but in the .9’s. In true standard scores, the mean will always equal 0 and the standard deviation will always equal 1.0.

To get TRUE standardized residuals, one must save the unstandardized residuals, then covert those to standard score form using that function with the SPSS Descriptives procedure (Analyze > Descriptive Statistics > Descriptives; then check “Save standardized values as variables.” If you create your standard scores in that fashion, you’ll find that the mean is 0 and standard deviation is 1.0.