Univariate spline function with interaction

by Prunus avium   Last Updated January 14, 2018 11:19 AM

I'm fitting a simple logistic model. Two covariates are described throughout a bivariate spline function defined with truncated linear basis (1 knots each). In this case I have:

  • three terms describing the two covariates and their interaction;
  • two terms for the two contrasts;
  • two terms for the interaction between the contrasts and the covariates;
  • one term for the interaction between the two contrasts.

Assuming that I want to check if the knot on one covariate is needed or not, since theoretically the two models are nested, the model above becomes:

  • three terms describing the two covariates and their interaction;
  • one term for the contrast;
  • one term for the interaction between the contrast and the other covariate.

Or should I also remove the last term (the interaction between the contrast and the other covariate)?

Thanks for your help.



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