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Let's say I'm using Baron & Kenny's method for mediation, which has the following requirements: (a path) IV has effect on mediator; (b path) mediator has effect on DV; (c path) IV has effect on DV; (c' path) when IV and mediator considered jointly, the effect of the IV is eliminated. Only the mediator has an effect on DV.

In an experiment I've run I exogenously manipulated someone's appearance in a photo. I theorized it would affect people's disgust, and subsequently their desire to be friends. There are very large effects for paths a-c (p all <.0001). However, when I run c', the effect of the mediator disappears (p=.2989) BUT the effect of the IV does not (p<.0001).

Now, if I were looking at the regression results without any knowledge of what the variables are, I would say "oh, I guess you made a mistake. Clearly what you have marked as the IV is the real mediator. Since the effect of the other variable disappeared when both were added, your 'IV' is soaking up the other variable's effect."

Which might be fair, except for one thing: it's theoretically impossible, since the IV in my experiment was exogenously manipulated. That interpretation would say "the level of disgust you have for that person causes them to have a different appearance in the photo, which changes how much you want to be friends."

How do I interpret these results?

Thank you so much for your help!

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    $\begingroup$ "if I were looking at the regression results without any knowledge of what the variables are": Please don't ever do statistics without knowing what the variables are. $\endgroup$
    – Robert Long
    Commented Aug 10, 2021 at 20:48
  • $\begingroup$ I apologize. I don't mean to seem like I'm doing statistics without knowing the variables. Hence the use of the subjunctive mood. What I mean is, if one were to look at that set of 4 regressions under a mediation paradigm, one would conclude appearance is the mediator, not disgust (c path becomes b path under that interpretation, and b becomes c). That, under Baron & Kenny's system, is what is happening. But that is impossible, knowing appearance is exogenous. Hence why I was confused. $\endgroup$
    – user332082
    Commented Aug 10, 2021 at 22:16

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You interpret it as the effect is not mediated by the mediator.

The mediator and the outcome are correlated because they share a common cause.

"I were looking at the regression results without any knowledge of what the variables are" - that's why you don't do this, or you'd conclude that lung cancer causes smoking and that laughing causes you to watch amusing videos on Youtube.

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  • $\begingroup$ Thank you for your response! Are you saying it seems like the IV causes the mediator and the DV, but independently of each other? That thought had crossed my mind, but there is quite a bit of other research maintaining that my mediator affects the DV. Re:my hypothetical interpretation, what I was saying is if one were to apply Baron & Kenny's criteria to those 4 regressions, one would come away saying appearance is the mediator. But that's impossible because appearance is exogenously manipulated. Hence my confusion. $\endgroup$
    – user332082
    Commented Aug 10, 2021 at 22:26
  • $\begingroup$ My understanding is that if you follow B&K you come away saying there's no mediation. Which is what you should say. You can't swap around your variable labels and then apply B&K. $\endgroup$
    – Jeremy Miles
    Commented Aug 10, 2021 at 23:10

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