Skip to content
Prev 9772 / 20628 Next
Original Raw

Changes of estimate sign when interaction effects are highly significant

Ben Bolker 
Adam Smith <raptorbio at ...> writes:
More precisely, with R's default treatment contrasts,
the main effects parameters in a model with interactions
refer to the expected change when the other continuous
predictors in the interaction are at zero and the other
categorical predictors are at their baseline level.

  The best thing to do is often to draw a graph so
you can see visually what's going on.  For two continuous
covariates it may be a good idea to use cut() [or
cut_interval() or cut_number() from the ggplot2 package]
to subdivide one of the covariates into range.

Thread (3 messages)

MORAN LOPEZ, TERESA Changes of estimate sign when interaction effects are highly significant Mar 5 Adam Smith Changes of estimate sign when interaction effects are highly significant Mar 5 Ben Bolker Changes of estimate sign when interaction effects are highly significant Mar 5