How can I compare the interaction terms of two separate polynomial regressions? Both regressions look like
y = x1 + x2 + (x1)^2 + (x2)^2 + x1*x2
Also, how can two interaction terms from the same regression be compared?
And how would you determine the statistical power for doing so?
Thanks!
Yes, x1*x2 is the interaction terms.
What do you mean with points? All variables will be measured at least on a six-point scale (questionnaire research), many of them on a 20 or 30 point scale.
How would you like (relative) interaction strength:
Interaction = | x1*x2 / (y - x1 - x2 - x12 - x22) | , or just
Interaction = | x1*x2 / y | ?
Thank you for your answers.
>Marek Gutowski: I am only using x1*x2 as in lm(y ~ x1 + x2 + (x1)^2 + (x2)^2 + x1*x2).
>Fausto Galetto: I am not sure how this is relevant, but to estimate a straight line, I use the intercept and slope as in y = ax + b or alternatively two points. I am referring to a typical polynomial regression in the social sciences with survey responses forming the variables.
Are you referring to the sample size? This was the second part of my question: How can I determine the sample size for a power of .90 and a medium size difference?
But for the moment, assume that it consists of at least 200 respondents, i.e., that the matrix is 200x2 with x1 and x2 being the columns.
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