Mediator variable RMANCOVA

#1
I have collected data to answer the question “Does Neuroticism Mediate the effect of a Mindfulness Intervention?” I Have collected pre-intervention Mindfulness Score and a post intervention measure (both scale). I also took a neuroticism score before the intervention to estimate the level of trait neuroticism (also scale). There was no control group. So far I have managed to demonstrate with a paired-samples t-test that there is a significant difference between pre and post-mindfulness scores, I have used Pearson correlation to show that mindfulness and neuroticism are negatively correlated at baseline (both of these are a replication of the existing findings). For the mediator part, I intended initially to use the model from another study which divided the neuroticism score into low, low/medium, medium high and high as a quasi-independent variable. However, the scores in my data were too clustered together without much of a range in the group (there was a high attrition rate ~45%) so these 4 groups are not possible. I have tried running a repeated measures ANOVA, where I dichotomize neuroticism into low/high, which I know is not the best idea as I will artificially restrict the variance in my data. This does however produce quite a sensible looking plot and desirable output for my study but I know it's not sound practice. I have also tried doing what I think is a repeated measures ANCOVA, with time at 2 levels as a within subjects factor (pre and post-intervention score) and neuroticism as a covariate but I have nothing to put into the between subjects factor so I’m not sure if it’s accurate. It is giving neuroticism a value of 3.45 in the model but I have no idea what that number means or how to interpret it. It also produces a sensible looking plot showing the increase in mindfulness pre to post-intervention. I have also tried is computing a mindfulness score difference and correlating that with the level of mindfulness which also gives me a medium size positive correlation <0.05. Any help would be greatly appreciated as I am really desperate! help1.png help 2.png
 

Karabiner

TS Contributor
#2
Mediation would mean: The Intervention changes the degree of neuroticism,
and through this, the intervention exerts its influence on the dependent variable
(mindfulness). The change between pre-mindfulness and post-mindfulness
is mediated by a change between pre-neuroticism and post-neuroticism.

But you seemingly only have pre-neuroticism scores? And whether a trait-measure
would be an appropriate mediator variable in the analysis of a mindfulness interventon,
seems doubtful. Are you sure that you really mean mediation here, not moderation?

Regarding theat categorization stuff, I don't know what should be the use of it. One
can just use the scores from the original measurement scale.

With kind regards

Karabiner
 
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#3
Hi Karabiner,

Thank you for your reply,

I think you are right, I am confused about moderators and mediators. How might I got about this analysis ?

With kind regards,

Nick
 

Karabiner

TS Contributor
#4
Reprated-measures analysis of variance with neuroticism as additional predictor. The interaction
between the repeated-measures factor and the neuroticism score represents the moderatiing effect
of neuroticism on the intervention effect.

With kind regards

Karabiner
 
#5
Thank you. So is the configuration in the picture above correct? What does the value of 3.45 on the graph represent as a statistic?

Kind regards

Nick
 

Karabiner

TS Contributor
#6
Of interest for you (at least AFAICS) is the output of the ANOVA, and in it the interaction effect.
If you want to visualize what is going on, you could split your sample for example into 3 groups (lowest
33% of neuroticism scores, medium 33%, highest 33%), and plot pre- and post "mindfulness" values
for these three groups. Then you can see, for example, whether the change from pre to post ist larger
for the lowest neuroticims group than for the highest.

With kind regards

Karabiner
 
#7
Thanks Karabiner,

Unfortunately my sample is too small and scores are too homogeneous to split these scores appropriately.
I really appreciate your responses and help though!

Kind regards,

Nick
 
#9
Mediation would mean: The Intervention changes the degree of neuroticism,
and through this, the intervention exerts its influence on the dependent variable
(mindfulness). The change between pre-mindfulness and post-mindfulness
is mediated by a change between pre-neuroticism and post-neuroticism.

But you seemingly only have pre-neuroticism scores? And whether a trait-measure
would be an appropriate mediator variable in the analysis of a mindfulness interventon,
seems doubtful. Are you sure that you really mean mediation here, not moderation?

Regarding theat categorization stuff, I don't know what should be the use of it. One
can just use the scores from the original measurement scale.

With kind regards

Karabiner
Good day!

I am doing a similar study, but let's continue using this example. In my case, I DO have the post-neuroticism scores, and I AM doing a Mediation analysis, not a moderation analysis (although I will be doing it later in the study, for now, I would just like to do a mediation analysis). Do I then use the difference in the pre- and post-neuroticism scores for the mediation? I am using the PROCESS Macro for SPSS. If you could please help me with this issue, it would be appreciated!

Kind regards
Elle