Drawing a graph with insignificant*coefficient!

[Eldar Saleh]

Hi,

Can we draw a graph when some of our regression coefficients show up as insignificant?
Specifically, I have estimated a quadratic moderation relationship in which only the interaction effect and the coefficient of the independent variables were significant. Then I wanted to plot a curve using the Johnson-Neyman toolbox

Consider for example these two equations:
Eq 1. Y = a + b1*X + b2*X^2 + e
Eq 2. Y = a + b1*X + b2*X^2 + b3*W + b4*X*W + b5*X^2*W + e
where, Y is DV (Dependent Variable), X is IV (Independent Variable), and W is the moderator.

I really doubt whether I can plot these equations when b1 is insignificant in Eq1, and b2, b3, and b4 are insignificant in Eq2.
I understand that the above questions include separate issues. First, I don't want to use the result of this discussion for the matter of inference. It is just for representing a graph to facilitate communication. Second, Equations 1 and 2 are different, apparently. However, the issue is if we are going to insert data into variable X, can are we allowed to do it for terms whose coefficients are insignificant?

Thank you in advance.

[Clyde Schechter]

In a quadratic model, the coefficient of the linear term says nothing whatsoever about the "significance" of the variable X in the model. In fact, all it tells you is whether the location of the parabola's axis of symmetry is located nearer to or farther from the y-axis! It is a very rare research question indeed that would lead one to care about that. When dealing with a quadratic model, you should never consider the linear term in isolation. If you must worry about the "significance" of the X variable, that has to be based on a joint test of the linear and quadratic terms--never on either alone.

[Eldar Saleh]

Thank you Clyde!

I am surprised that after editing the title of my post it has been sent twice. So would we please continue our discussion under the other post?