## Interaction effect significant, both main effects not

zypriafl
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Joined: Sat Jul 15, 2017 3:20 pm
Real name and title: B. Sc. Florian Zyprian

### Interaction effect significant, both main effects not

Dear Community,

in my PLS-Model I am using a Interaction Effect(using SmartPLS Moderating Effect). The Boostrapping Analysis shows a significant Moderation Effect, whereas both main effects are not significant.

I am wondering if (and how) I can interpret the significant Moderating Effect in this case?

jmbecker
SmartPLS Developer
Posts: 1129
Joined: Tue Mar 28, 2006 11:09 am
Real name and title: Dr. Jan-Michael Becker

### Re: Interaction effect significant, both main effects not

The moment you include an interaction effect, the effect of A and B on X are not main effects anymore, but conditional effects or simple effects.

The equation that you estimate is then: X = (p1 + p3 ·B) · A + p2 · B which is equivalent with X = (p2 + p3 ·A) · B + p1 · A or X = p1 · A + p2 · B + p3 (A · B)

p1 (the simple effect or conditional effects) is the effect of A on X, when B is zero (because then p3 is ignored). As we use standardized data in PLS (which includes centering), B is zero at the sample mean of B.
With a significant interaction effect (p3) your overall effect of A on X (p1 + p3·B) might be insignifcant when B is zero (p1), but signficant if B is large (e.g., 2*p3) or small (e.g., -3*p3).
Dr. Jan-Michael Becker, University of Cologne, SmartPLS Developer
Researchgate: https://www.researchgate.net/profile/Jan_Michael_Becker
zypriafl
PLS Junior User
Posts: 4
Joined: Sat Jul 15, 2017 3:20 pm
Real name and title: B. Sc. Florian Zyprian

### Re: Interaction effect significant, both main effects not

@jmbecker Thanks for the kind reply.

Does anybody know a published paper, that interpreted these kind of interaction effect?

Thank you
josemesquita
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Joined: Sun May 19, 2019 1:34 pm
Real name and title: Jose Mesquita, Professor

### Re: Interaction effect significant, both main effects not

Dear Zypriafl, did you find any published paper? I'm dealing with a similar issue.

Jose Mesquita
zypriafl
PLS Junior User
Posts: 4
Joined: Sat Jul 15, 2017 3:20 pm
Real name and title: B. Sc. Florian Zyprian

### Re: Interaction effect significant, both main effects not

I found these papers to be somehow related to this isssue:

Belsky, J., Pluess, M., & Widaman, K. F. (2013). Confirmatory and competitive evaluation of
alternative gene‐environment interaction hypotheses. Journal of Child Psychology and
Psychiatry, 54(10), 1135-1143.

Grainger, J., Muneaux, M., Farioli, F., & Ziegler, J. C. (2005). Effects of phonological and
orthographic neighbourhood density interact in visual word recognition. The Quarterly
Journal of Experimental Psychology Section A, 58(6), 981-998.

Oh, I. S., Lee, K., Ashton, M. C., & de Vries, R. E. (2011). Are Dishonest Extraverts More
Harmful than Dishonest Introverts? The Interaction Effects of Honesty‐Humility and
Extraversion in Predicting Workplace Deviance. Applied Psychology, 60(3), 496-516.
josemesquita
PLS Junior User
Posts: 5
Joined: Sun May 19, 2019 1:34 pm
Real name and title: Jose Mesquita, Professor

### Re: Interaction effect significant, both main effects not

Thank you, I'll try to find them.
josemesquita
PLS Junior User
Posts: 5
Joined: Sun May 19, 2019 1:34 pm
Real name and title: Jose Mesquita, Professor

### Re: Interaction effect significant, both main effects not

Does anyone could help me in the following issue:

In my model, I'm measuring the effects of complaint satisfaction (CS) and relational switching costs (RS) on switching intention (SI).

Without moderation the main effects are:

CS>>>>SI, negative and significant;
RS>>>>SI, negative, non significant.

When I include the moderation effect of RS on CS (RS*CS), the interaction effect is not significant, but the simple effect becomes significant.

I've never seem such a result and I'm not sure how to explain it.

Jose Mesquita
jmbecker
SmartPLS Developer
Posts: 1129
Joined: Tue Mar 28, 2006 11:09 am
Real name and title: Dr. Jan-Michael Becker

### Re: Interaction effect significant, both main effects not

Usually the literature suggests that when the interaction effect is not significant, you should not interpret the simple effects, but only the main effects. Likewise, if the interaction is significant you should not interpret the main effects, but only the simple effects.

However, sometimes it may also happen that the interaction effect has a small to medium effect size and is close to being significant and you may only have insufficient power (not enough observations) to find it significant. Of course, it is hard to tell whether such a situations is really present.
Dr. Jan-Michael Becker, University of Cologne, SmartPLS Developer
Researchgate: https://www.researchgate.net/profile/Jan_Michael_Becker
josemesquita
PLS Junior User
Posts: 5
Joined: Sun May 19, 2019 1:34 pm
Real name and title: Jose Mesquita, Professor

### Re: Interaction effect significant, both main effects not

Thank you Prof. Becker
mafakhimi
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