as i know, increasing a positive effect means it will be more positive and increasing a negative effect it will be more negative ( not less negative as you mentioned) . please correct me if i'm wrong. i am getting confused
But your confusion is natural. Many people think that increasing a negative means making it more negative. That's not correct English usage, but it's common. That's why describing things in this way is a recipe for confusion. Even after it becomes clear in your own mind, the likelihood that other you communicate your results to will misunderstand is high. That's why I think it's better to avoid short summaries like that and speak about specific numbers or show graphs. That leaves no room for misunderstanding.
Re #14: you are getting confused because you are thinking you have two models like this:
Code:
Y = B0 + B1 X1 Y = B0 + B1 X1 + B2 X2 + B3 X1*X2
Code:
Y = C0 + C1 X1 Y = B0 + B1 X1 + B2 X2 + B3 X1*X2
Most important, these models are not alternative valid descriptions of a single reality. They are inconsistent with each other, and if either is correct the other is incorrect, except in the very unusual case where B2 and B3 are zero, or close enough to 0 to ignore. You do not get to choose between these models. At most one of them is a satisfactory description of the data generating process.
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