constraining interactions to include a specified variable
Chris Habeck <habeck.cw at ...> writes:
I am trying to constrain interactions within a model to always include a particular variable of interest and to limited interaction complexity to three-way. The later is straight forward, for example: lme(response ~ (a + b + c + d + e + f)^3) However, my goal is to constrain all 3-way interactions to always include variable "a". Is there efficient code for this problem?
Would something like response ~ a*(b+c+d+e+f)^2 work for you? Ben Bolker