[R-sig-eco] NMDS axes scores

[Jari Oksanen]

> On 11 Jan 2016, at 14:13 pm, Bob O'Hara <bohara at senckenberg.de> wrote:
> 
> 
> Whilst I'm filling bandwidth, I'm not sure Jari's suggestion that you need the interaction term is correct. If a model is linear in axis1 and axis2, then any rotation is also linear, i.e. the transformation is c_1 axis1 + c_2 axis2. So you only need Y ~ axis1 + axis2. Basically, it's still plane. The interaction adds a curve: if you want that you also need to include quadratic terms, i.e. Y ~ axis1 + axis2 + axis1^2 + axis2^2 + axis1:axis2.
> 
Me neither: I think my suggestion to include interaction term was wrong. This belief seems to be shared by vegan authors who define linear trend surface without interaction in ordisurf().

Cheers, Jari O.