I am attempting to run an exponential decay model in nlme with 3 fixed
and random effects (an initial value, an asymptote, and a decay rate). I
am having trouble getting convergence now that I have added the
asymptote to the model, so I was attempting to specify start values for
the random effects. I have 161 groups (SUBJECT) and have constructed a
161 x 3 matrix (E) for the random effects start values. However, I
receive the following error message:
> fm3 <- nlme(model = RASCH16A ~ B + A*(exp(-K*DAYS)),
+ fixed = B + A + K ~ 1,
+ data = rasch,
+ random = B + A + K ~ 1 | SUBJECT, groups = ~SUBJECT,
+ start = list(fixed = c(20, 68, 0.03), random= E))
Error in nlme.formula(model = RASCH16A ~ B + A * (exp(-K * DAYS)), fixed
= B + :
groups levels mismatch in random and starting values for random
at level SUBJECT
Does anyone have any ideas as to what might be triggering this error
message?
Thanks if you can help~
Lindsey Root