[R] Interaction plot between 2 continuous variables

[Ben Bolker]

Bert Gunter <gunter.berton <at> gene.com> writes:

> 
> This almost certainly has nothing to do with mixed effects models per
> se. x1 and x2 are probably ( if what you see is not due to a few
> unusual values) correlated, so the standard decomposition into main
> and interaction effects does not have the usual meaningful
> interpretation (e,g, that you would get from orthogonal regressors).

  See also

http://stats.stackexchange.com/questions/5450/
  what-if-interaction-wipes-out-my-direct-effects-in-regression/

(URL broken to make gmane happy)