[R] Specifying interactions in rms package... error

I am encountering an error I do not know how to debug. The error arises when I try to add an interaction term involving two continuous variables (defined using rcs functions) to an existing (and working) model. The new model reads: model5 - lrm( B_fainting ~ gender+ rcs(exactage, 7) +

Re: [R] Specifying interactions in rms package... error

On Aug 2, 2010, at 9:06 PM, Rob James wrote: model5 - lrm( B_fainting ~ gender+ rcs(exactage, 7) + rcs(DW_nadler_bv, 7) + rcs(drawtimefrom8am, 7)+ DW_firsttime+ DW_race_eth + rcs(DW_BPS, 5)+ rcs(DW_BPD, 5)+ rcs(pulse3, 5)+ locat2+ (rcs(exactage, 3) *

Re: [R] Specifying interactions in rms package... error

Hi Rob, rms wants symmetry in the sense that the interactions need to use the same number and location of spline knots as the main effects. So if using the * notation omit the main effects (which are generated automatically) and live with the equal knots. Or use the restricted interaction