Moderating Effects with Seemingly Uncorrelated Variables

I received a great question this week, as a submission to my Ask the Stats Make Me Cry Guy page, which asked: In order for a moderating relationship to exist, do the predictor IV and dependent variable need to be significantly correlated?". This is a question that I am asked a lot, partly because of the common confusion between mediators and moderators and the commonly held belief that an IV and DV should be related for mediation to be present (see my video blog on Mediators, Moderators, and Supressors for more info on this topic). However, moderators are a completely different story. In fact, a simple correlation between two variables can be very misleading, if one relies on it as an indicator of potential moderating effects and/or as an indicator that moderating effects should be tested.

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Within-Subject and Between-Subject Effects: Wanting Ice Cream Today, Tomorrow, and The Next Day…

The conceptual difference between within-subject and between-subject effects is something I am asked about quite often. So often in fact, I thought a blog posting was warranted! As a quick disclaimer, I know this is a complex issue and the description of what each type of effect actual is varies greatly based on the kind of analysis one is conducting. However, what follows is an attempt to provide a basic conceptual foundation to understand the differences.

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