Hi all,

can someone supply advice on this:

 

I am determined to analyse a 3 way interaction of variables a x b x c. No problem there. But since I'm using hierarchical multiple regression, I am following aiken and west's steps of centering my data to produce interaction terms, which is again fine. My query lies in producing the graphs to understand the signficant 3 way interaction that has been found.

 

I can (just about) easily do a 2 way interaction and represent that graphically. However, the problem is the way i do a 3 way interaction. Basically, I'm going to use the median split method of separating my sample on the 3rd predictor © to produce a high and low grouping. Then I'm going to rerun my analysis, having computed NEW centered variables based on the changes in the mean for variable c, again on the two separate groups using the initial hiearchical steps of the regression with main and interaction terms. Finally, I can produce two 2-way interaction graphs, one of high and one of low on predictor c.

 

Though I've seen this method done before (seen in research published in a journal), this is my question: If the initial full set of data produced a significant 3 way interaction, won't splitting the data into two and then rerunning the analysis (as noted above) remove the signficance? And therefore doing the graphs will come out with rubbish?

 

thanks for your help.

J

Splits always reduce predictive power. Whether or not it's rubbish depends on how granular your split and how much the variable you're splitting varies.