I am centering variables that enter interaction terms in my linear regression. To check the robustness of my results, I exclude certain cases from the original sample, and re-run the regression analysis in that modified sample.
Which of the following approaches to centering of the variables is more appropriate to compare the results of the regression analysis between the modified and original sample?
- use the means from the original sample for centering in both regression analysis; or
- use the means from the original sample for centering for the regression in the original sample, and use the means from the
modified sample for centering for the regression in the modified sample.
In the methods books I have consulted, notably Cohen, Cohen, Aiken & West (2003) and Tabachnick & Fidell (2007), as well as on the web, I have not been able to find a recommendation. I only found the following consideration:
If you do center, be consistent throughout, i.e. different sample selections could produce different means, so comparing results produced by different centerings could be deceptive. see Interpreting Interaction Effects; Interaction Effects and Centering