*“I'd like to mean center a lot of variables in order to compute interaction terms for a regression analysis. Is there an easy way to do this for many variables simultaneously?”*

## Mean Centering - What and Why

- This tutorial focuses on
*mean centering variables in SPSS*. However, we'll briefly introduce the concept first. - Mean centering a variable means subtracting its (arithmetic) mean from all its values.
- The result is that a mean centered variable has a mean of exactly zero. (Apart from that, its frequency distribution does not change.)
- Note that mean centering is also one of the two steps in
**standardizing**variables (computing their z-scores). - Mean centering without fully standardizing variables is usually done before computing
**interaction terms**in regression analysis. - Doing so decreases
**multicollinearity**between an interaction term and its corresponding main effects. It may also facilitate the**interpretation**of regression coefficients for the interaction terms.

## SPSS Mean Center Tool

SPSS Mean Center Variables Tool- Make sure you have the SPSS Python Essentials installed.
- Download and install Mean Center Variables. Note this is an SPSS custom dialog.
- Go to . Fill in the names of the variables you’d like to mean center.
- By entering a
**prefix**, mean centered variables will be created as new variables in the active dataset. With the prefix left empty, the original variables will be overwritten by their mean centered counterparts. - Click syntax. and run the pasted
- As a quick check, you could run
`DESCRIPTIVES`

on the mean centered variables to confirm that they all have zero means. - Clicking the tool's button will take you to this tutorial. We very much appreciate your feedback on it.

## This tutorial has 37 comments

## By Ruben Geert van den Berg on February 2nd, 2018

Thanks! Happy to hear you like it!

Keep up the good work ;-)

## By Yueyan on February 2nd, 2018

Useful guidance!