Specify model with polynomial interaction terms up to degree n
On Jul 2, 2012, at 9:29 AM, YTP wrote:
I would like to specify a model with all polynomial interaction terms between two variables, say, up to degree 6. For example, terms like a^6 + (a^5 * b^1) + (a^4 * b^2) + ... and so on. The documentation states The ^ operator indicates crossing to the specified degree. so I would expect a model specified as y ~ (a+b)^6 to produce these terms. However doing this only returns four slope coefficients, for Intercept, a, b, and a:b. Does anyone know how to produce the desired result? Thanks in advance.
You might try: poly(a,6)*poly(b,6) (untested ... and it looks somewhat dangerous to me.)
David Winsemius, MD West Hartford, CT