I was wondering if you can include an interaction term as a predictor with the density surface modeling in Distance 6.1? The "help" index has 2 suggestions--either create a new field and multiply the predictor values together beforehand or use a:b or a*b when specifying the model formula. I would like to use the latter suggestion so I have more options for plotting the terms with the response variable either in Distance or R. However, I have tried including various combinations of my 2 interaction terms, such as ~s(a*b), ~s(a,b), ~s(a:b), ~s(a)*(b) without much luck. I either get an error message (ie-model has repeated 1-d smooths of same variable) or it runs with no errors, but the resulting surface plots don't make biological sense. One term is linear and the other is non-parametric--this could be part of the problem? I'm hoping there is a way to do this besides separating my data into 2 groups and analyzing them separately. Thanks so much for any suggestions!
distance-sampling list home page:
To unsubscribe, go to the home page and click "Join or leave the list",
or email [log in to unmask] with the following message body:
Before posting to the list, read the list guidelines at
Any questions, email the list owner at
[log in to unmask]