Removing variables from multiple regression

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Removing variables from multiple regression

Karen Wood

Hi all, I'm in a bit of a dilemma,


I'm  explaining variance in English scores, using Hierarchical multiple regression.

I have three intelligence variables and I am adding Interests variables to see if interests are able to explain additional variance after accounting for intelligence.
Artistic interests are able to explain an additional 6.5% of variance . One of the three intelligence variables (Raven's matrices) does not add significant variance, nor does it appear to be acting as a suppressor variable on the other variables in the regression.

If I remove the intelligence variable not contributing to the explained variance, the sample size changes from N = 98 to N = 109, as not all of the participants have completed the Raven's matrices.
On the removal of Raven's,  Artistic interests explain only 2.3% of additional variance which is not significant. HOWEVER, If I keep the sample size constant at N = 98 by adding Raven's in the last step of the regression , Artistic interests explain an  additional 6.7% of variance .

My dilemma , is that I've only just discovered this difference and have already completed my analysis (I was editing and re-checking!!) . So do I re-do my analyses, so that every time Raven's is removed" (and this is often!) it is "left in" by adding it in  the final step of the analysis.
I think I already know what I will be doing. ....re-running the analyses!!

I was hoping someone could convince me that I should just leave it as is, provided I record the different sample sizes.

Karen

PS: Aren't Statistics fun!!