It's quite counter-intuitive, that the positive main effects of IV.1.gm
and IV.2.gm
are changed into negative effects on the dependent variable when I tested the interactions. Note that all variables are standardized, and there's no multicollinearity issue. IV.1.gm is group-mean centered and IV.2.gm is grand-mean centered as I learned in the stat class.
The visualization shows there are positive interaction effects. Then why do they show negative interaction terms in the regression table?
*I did the test again without standardization. The results are the same so I didn't attach them here. But the interaction plot looks different.
But isn't it still look like a positive interaction plot? I am still confused about why regression coefficients for interaction term is negative.