

Testing Level1 moderator on Level2 ... 

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Mo Wang posted on Wednesday, July 01, 2009  2:38 am



Hi all, I have a question regarding how to test crosslevel moderation when the hypothesized moderator is at Level1 instead of Level2. Assuming at Level2 (e.g., grouplevel) I have a variable C and Level1 (e.g., individual level) two variables X and Y. I have a theorybased hypothesis that C will have a crosslevel main effect on Y and this effect will be moderated by X. How to test this moderation effect? Shall I just estimate how C influence the random slope between X and Y at Level1 as if I hypothesize that C moderates the main effect of X on Y? My concern is that when we are testing crosslevel moderation in this way, we are really only testing how the level2 predictor influence the random slope at level1. It is not like in OLS where the testing of interaction is symmetric (i.e., for an interaction term XY, you can interpret either as X moderating Y or Y moderating X). I am wondering whether this symmetric interpretation exists in crosslevel moderation test as well. If so, can anyone provide me some references? Thanks! Mo 


Yes, a random slope for y on x where c predicts this random slope seems to be a standard crosslevel interaction. See our course handout for Topic 7, slide 42, on our web site. I guess it would only be symmetric if there is no level 2 residual variance for the random slope regressed on c  otherwise it is x that multiplies that level 2 residual, not c. I don't know about references  does anyone else? 

Mo Wang posted on Thursday, July 02, 2009  2:02 am



Thank you for your response, Bengt. So, for my scenario (i.e., level1 variable moderating level2 effect), shall I just form a level2 X and use the product of it and C to test the moderation effect? Mo 


No, you don't form a product of variables. Instead, see UG ex9.2 for how to handle this. 


So, just to confirm that I correctly understand Bengt's reply to Mo on July 2, 2009: It makes NO DIFFERENCE whether you're testing ... a) the moderating effect of C on the association between X and Y, or b) the moderating effect of X on the association between C and Y. You use the SAME TEST to answer both questions. Namely, you model the slope of Y on X as random, and then regress that slope on C. Correct? Thanks, Lois Downey 


Yes. 

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