I have a very basic understanding of statistics, and have done many correlations and regressions or simple t-tests, but never an interaction and it is confusing me a bit. I only need to understand the basics of it for now and would really appreciate any input from all you statistics experts.

I just basically need to understand what an insignificant interaction means, when the main effects and the conditional effects are all significant.

I am using modprobe syntax (Hayes, 2010) for SPSS to test an interaction between 3 variables.

I have 3 variables they are:

Outcome Variable
 InterVio (Inter Group Violence) (scale from 0-13)

Focal Predictor Variable
 Ruminati (Rumination) (Scale from 1-4)

Moderator Variable
 ColNarc (Narcissism) (Scale from 1-6)

The hypothesis (simple psychology report hypothesis) is: That narcissism and rumination interact at high levels to predict higher aggression and interact to predict lower aggression at lower levels.

The overall model shows significant main effects, but insignificant interaction:

Complete Model Regression Summary
       R-sq          F        df1        df2          p          n
      .3726    28.7066     3.0000   145.0000      .0000   149.0000

                  b         se          t          p
constant     -.0407      .6950     -.0585      .9534
Ruminati      .6450      .2777     2.3229      .0216  <----
ColNarc       .5646      .2258     2.5000      .0135  <----
interact     -.0690      .0838     -.8237      .4114  <----

Interact is defined as:
 Ruminati X        ColNarc


I quite simply want to report this interaction in a psychology research report (basic one).

I just do not understand how to interpret the insignificant interaction. I think I could say that "the IVs predict the DV independently but the interaction was not significant (therefore it is by chance that at different levels of one IV the second IV and the DV increase?)

But then the output shows 'the conditional effect of focal iv at values of the moderator iv'.

Conditional Effect of Focal Predictor at Values of the Moderator Variable
    ColNarc          b         se          t          p    LLCI(b)    ULCI(b)
     2.2472      .4900      .1169     4.1920      .0000      .2590      .7210
     3.2077      .4237      .0903     4.6905      .0000      .2452      .6023
     4.1682      .3574      .1249     2.8614      .0048      .1105      .6043

Alpha level used for confidence intervals:

Moderator values are the sample mean and plus/minus one SD from mean

My problem is that these are significant and therefore makes me wonder what they mean. Because if the entire interaction is insignificant (occurred by chance, as I understand) how can it still interact significantly at different values? (So would I ignore the interaction significance and just report the conditional effects and the slope plot?)

Also does this table mean that the slope line plot graph would be statisticall significant? (But how can it be if the interaction is insignificant? Its so confusing for me, how anything can be significant if the interaction isnt...)

Basically it would be great if someone could just tell me what the significance of the last table actually is meant to be telling me.

Also I was wondering if marginal effects could mean the same thing as conditional effects?

Edited to Add: I have supposedly enough literature to support this interaction existing, so maybe I should run a mediation instead after I find the insignificant interaction? Sorry for rambling everyone, but Im just getting more and more confused....

Thank you very much for anyone who bothers to even read this. I feel useless at stats sometimes.

  • $\begingroup$ Seems you've recreated your account and duplicated your previous question... $\endgroup$ – Nick Stauner Jul 1 '14 at 4:12
  • $\begingroup$ Hi, actually my other account was unregistered and i couldnt access the question when i got to my computer, so i tried to register the account by making an account with the same name and it didnt work. Also im new to this site and after looking at other questions i realised that mine was more yahoo answers standard and not very clear so i wanted to edit it (not that its much clearer now), but still couldnt so re wrote it here. $\endgroup$ – red Jul 1 '14 at 14:02

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