There are several nonlinear models for analyzing repeated measurements. The mean response for an individual depends on the regression parameter specific to that individual. One of the simple form is the sum of a vector of fixed parameters and a vector of random effect. In this paper, we give a confidence region of the fixed parameters approximately.
"Confidence regions of parameters in a nonlinear repeated measurement model with mixed effects." Hiroshima Math. J. 37 (1) 111 - 117, March 2007. https://doi.org/10.32917/hmj/1176324098