In specifying a crossed mixed effects model, I am trying to include interactions. However, I get the following error message:
Error in lme.formula(rate ~ nozzle, random = ~nozzle | operator, data = Flow) : nlminb problem, convergence error code = 1 message = iteration limit reached without convergence (10)
The model has the following: 1. 3 nozzle types (fixed effect) 2. 5 operators, each with 3 repeat measures on fuel flow from the 3 nozzle types.
I was asked to include the interaction between nozzle type and operator in the model. This is my code for the model:
flow.lme <- lme(rate ~ nozzle, error= nozzle|operator, data=Flow)
Why would I get this error message??