Hi there,
I am attempting to analyse data from a crossover study using a mixed
effect Emax model in R using nlme. I am having problems ascertaining how
to fit the model.
Subjects are randomly assigned to 1 of 4 treatments in a complete block
design. The response variable of interest is recorded once within each
period. So, subjects have a response for each period.
Specifically, I want to fit fixed effects: two continuous baseline
covariates (base1 and base2) and period which has levels 1-4. Subject
will be fitted as a random variable.
I have started with the 3 parameter Emax model using nls, with no other
covariates and no random term. The syntax of this I know to be correct.
When I progress to nlme, firstly fitting subject as random, I get
nonsensical answers for Emax and ED50. Even if I was getting reasonable
answers at this point, I am not sure how I specify period, a co-factor
in the model?
Hoping someone can help.
Many thanks in advance.
B Surujbally
LEGAL NOTICE
Unless expressly stated otherwise, this message is confidential and
may be privileged. It is intended for the addressee(s) only. Access
to
this e-mail by anyone else is unauthorised. If you are not an
addressee, any disclosure or copying of the contents of this e-mail
or
any action taken (or not taken) in reliance on it is unauthorised
and
may be unlawful. If you are not an addressee, please inform the
sender
immediately.
Pfizer Limited is registered in England under No. 526209 with its
registered office at Ramsgate Road, Sandwich, Kent CT13 9NJ
[[alternative HTML version deleted]]
